Using the custom tax rule, you can calculate tax rate by querying from a database table. Using a database table allows handling complex and large tax dataset.

The following example assumes you have a custom tax table called "Taxes" in your DNN database with these columns:

• ZipCode - varchar 5 digit zip code
• Rate - decimal tax rate to multiply against the amount (e.g. "0.10" for 10%")

Since XSLT cannot access the database directly, we will need a middleware code file that will access the database in its place. Follow the steps below:

1. Create an .aspx file (e.g. TaxRate.aspx") with the following code. You may need to modify the names to match your table and column names:
    

   <%@ Page Language="C#" AutoEventWireup="true" %>
<%@ Import Namespace="System.Data.SqlClient" %>
<%@ Import Namespace="System.Configuration" %>
<%
    Response.Clear();

    // The Zip code will be passed through the query string
    var zipCode = Request.QueryString["zipcode"];

    // Sanitize zip code
    if (!String.IsNullOrEmpty(zipCode))
        zipCode = zipCode.Replace("'", "''");

    // Assume you have a Taxes table with a ZipCode and Rate columns
    var sql = "SELECT Rate FROM Taxes WHERE ZipCode = '" + zipCode + "'";
   
    using (SqlConnection connection = new SqlConnection(ConfigurationManager.ConnectionStrings["SiteSqlServer"].ConnectionString))
    {
        connection.Open();

        SqlCommand command = new SqlCommand(sql, connection);
        using(SqlDataReader reader = command.ExecuteReader())
        {
            // Return tax rate or zero if not found
            if (reader.Read())
                Response.Write(reader[0]);
            else 
                Response.Write("0");
        }
    }
%>

2. Deploy the file to your Web site's root folder. Make sure the file is reachable by using your browser and passing a valid zip code (e.g https://site/TaxRate.aspx?zipcode=90210)
3. Under Storefront administration Configuration > Taxes, add a new tax method. Give it a name like "Tax table".
4. Choose Custom Rate type and Custom Rule for the rate rule.
5. Paste the following XSL rule in the Rule view.
   
   <xsl:transform xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="2.0">
  <xsl:template match="/">
    <!-- Retrieve the tax rate by HTTP request -->
    <xsl:variable name="rate" select="unparsed-text(concat('https://site/TaxRate.aspx?zipcode=', substring(/in/salesOrder/billingPostalCode, 1, 5)))"/>
    <out>
      <taxAmount1>
        <xsl:value-of select="$rate * /in/this/salesOrderDetail/(amount + discountAmount)"/>
      </taxAmount1>
      <taxAmount2>0.00</taxAmount2>
      <taxAmount3>0.00</taxAmount3>
      <taxAmount4>0.00</taxAmount4>
      <taxAmount5>0.00</taxAmount5>
    </out>
  </xsl:template>
</xsl:transform>
6. Modify the XSL rule to replace the example URL with your own URL.
7. Save and test.