multiplying textbox values
===

Problem: I have 3 text boxes:subtotal, tax, and total. I want the value in the subtotal text box to be multiplied by the value in the tax textbox and be displayed in the total text feild.

I have created a JS Fiddle but i cant seem to get my code to work in it! 
You can see the subtotal working perfectly on my site!

Js fiddle http://jsfiddle.net/thetylercox/SQr2C/2/

My site http://soldbybillcox.com/treasure/demo.php

     <input  class="txt1" type="text" name="subtotal" value="" id="subtotal" size="16">.
     <input  class="txt1" type="text" name="tax"  id="tax" value="" size="16">
     <input  class="txt2" type="text" name="total1" value="" id="total1" size="16">

Currently i have this which I though would work!

      $(document).ready(function() {
       calculateSum();
      $(".txt").each(function() {
        $(this).keyup(function() {
            calculateSum();
        });
      });
     });

     function calculateSum() {
     var sum = 0;
     $("#sum").val(sum.toFixed(2));
     //iterate through each textboxes and add the values
     $(".txt").each(function() {
        //add only if the value is number
        if (!isNaN(this.value) && this.value.length != 0) {
            sum += parseFloat(this.value);
        }
    });
    $("#sum").html(sum.toFixed(2));
    var subtotal = document.getElementById("subtotal").value == "";
    var subtotal = document.getElementById("subtotal").value = sum;
    <!--end adding script subtotal -->

     <!--TAXES -->

      function getTax(tax) {
        var taxFloat = parseFloat(tax)
        if (isNaN(taxFloat)) {
            return 1;
        } else {
            return taxFloat;
        }
     }

     var total = getTax($('#tax').val()) * sum;
     var total1 = document.getElementById("total1").value = total;
     <!--
     end Taxes -->
     }​

     