Please see Getting Started for help with using the KampData TaxEngine.

using System;
using System.Runtime.InteropServices;
using System.Collections;
//Add the KDTaxEngine.dll as a reference.
using KampData.TaxEngine.API;
using KampData.TaxEngine.API.Enums;

namespace TaxEngineConsoleApp
{
    /// <summary>
    /// This sample uses hardcoded values to illustrate what is required
    /// to retrieve the tax schedule and tax option for a line item
    /// using the DynamicZip Tax by Item Category settings.
    /// </summary>
    /// <remarks>To use the KampData TaxEngine in this sample, or in any other 
    /// project, you must first setup the SOP module from the KDControlCenter.exe's 
    /// Transaction Source Module Setup window. Please see "Getting Started"in the 
    /// KDTaxEngine.chm help file for more information.</remarks>
    class CSharpClient
    {
        [STAThread]
        static void Main(string[] args)
        {
            bool abort = false;
            ArrayList cities = new ArrayList();
            ArrayList counties = new ArrayList();
            ArrayList states = new ArrayList();
            string server = @"Microsoft SQL Server";
            string userId = "User";
            string password = "p@ssw0rd";
            string companyDatabase = "TWO";
            string systemDatabase = "DYNAMICS";
            Int16 timeOutSeconds = 60;
            bool displayProgessBar = true;
            string loginMessage = "";
            string message = "";
            /// KampData.Portal object must be instantiated.
            Portal txEngn = new Portal();
            try
            {
                try
                {
                    /// The Portal.Login method makes the connection to SQL Server and
                    /// prepares the TaxEngine for use.
                    loginMessage = txEngn.Login(server, userId, password, systemDatabase, companyDatabase, timeOutSeconds, displayProgessBar);
                }
                catch (Exception e)
                {
                    loginMessage = e.Message;
                }
                if (loginMessage != "")
                {
                    abort = true;
                    Console.WriteLine(loginMessage);
                    Console.WriteLine("Press enter to continue");
                    Console.ReadLine(); // to hold window open displaying error message
                }
                if (!abort)
                {
                    /// Set the docType and module using the values you have setup
                    /// in the KDWindowClient.exe's Transaction Source Module Setup 
                    /// and Document Type Setup windows.  In the SOP module, invoices are 
                    /// docType 3.
                    /// (The SOP module can be setup automatically using 
                    /// File > Create SOP in the TE Transaction Source Modules window.)
                    Int16 docType = 3;
                    string module = "SOP";

                    /// You must assign a document number at this point. You can use a
                    /// document number generated by your order entry software
                    /// that will call the TaxEngine, or you can use the following code
                    /// to generate a document number.
                    string docNumber = txEngn.NextDocumentNumber(module);

                    /// Initialize the document.
                    txEngn.Document(docNumber, docType, module);

                    /// DocSaleOrPurchase defaults to Sales, so the following line
                    /// is unnecessary. However, you can set it to Purchases if desired.
                    txEngn.DocSaleOrPurchase = SalesOrPurchases.Sales;

                    /// A customer ID is required to check customer taxable status
                    /// to see if the customer is taxable or exempt. If no
                    /// customer ID is provided, the customer is assumed taxable.
                    txEngn.DocCustomerID = "ADAMPARK0001";

                    /// We now add a line to the order. The addressing and taxation 
                    /// features occur on the line level.  This step is required to 
                    /// instantiate a line object to work with. 
                    int lineNumber = 1;
                    txEngn.LineAdd(lineNumber);
                    // Set the values necessary to retrieve the item category taxability.
                    string itemCategory = "FREIGHT";
                    txEngn.LineItemCategory = itemCategory;
                    string zip = "84101";
                    txEngn.LineZip = zip;
                    string state = "UT";
                    txEngn.LineState = state;
                    string city = "Salt Lake City";
                    txEngn.LineCity = city;
                    string county = "Salt Lake"; // leave blank if unknown.
                    if (county != "")
                        txEngn.LineCounty = county;
                    txEngn.LineTaxScheduleSelect();
                    // The item tax schedule and item tax option should now be available.
                    Console.WriteLine("Line-item or document tax schedule [{0}] {1}",
                        txEngn.LineTaxScheduleID, txEngn.LineTaxScheduleDescription);
                    Console.WriteLine("Tax Option: {0}", txEngn.LineItemTaxOption);
                    if (txEngn.LineItemTaxScheduleID != "")
                        Console.WriteLine("Item tax schedule [{0}]",
                            txEngn.LineItemTaxScheduleID);
                    // The following is informational only - to show more results.
                    txEngn.LineItemUnitPrice = 100;
                    txEngn.LineItemQuantity = 1;
                    txEngn.DocCalculateTax();
                    Console.WriteLine();
                    message = "ID";
                    message = message.PadRight(80);
                    message = message.Insert(17, "Description");
                    message = message.Insert(48, "Total");
                    message = message.Insert(58, "Taxable");
                    message = message.Insert(68, "Tax");
                    message = message.Trim();
                    Console.WriteLine(message);
                    // This code displays the Microsoft Dynamics GP tax details
                    // that were used.
                    foreach (TrxTaxDetail trxDtl in txEngn.DocTaxDetails(TaxDetails.Transaction))
                    {
                        message = trxDtl.ID;
                        message = message.PadRight(80);
                        message = message.Insert(17, trxDtl.Description);
                        message = message.Insert(48, trxDtl.TotalAmount.ToString());
                        message = message.Insert(58, trxDtl.TaxedAmount.ToString());
                        message = message.Insert(68, trxDtl.TaxAmount.ToString());
                        message = message.Trim();
                        Console.WriteLine(message);
                    }
                    Console.WriteLine();
                }
            }
            catch (Exception exc)
            {
                Console.WriteLine(exc.Message);
                Console.WriteLine("Press enter to continue");
                Console.ReadLine(); // to hold window open displaying error message
            }
        }
    }
}