title: How to calculate tax percentage in jQuery?
body: <p>This is my first time asking a question here, so I hope I'll do it correctly.</p>
  
  <p>Just to give context, I'm developing a small website where lawyers can buy a digital version of some legal documents, but I'm having trouble calculating tax on the total cost. </p>
  
  <p>The taxes are calculated with two rates used in the province of Quebec, Canada: GST (5%) and QST (9.975%). Both rates are calculated using the subtotal amount. Here's what I tried so far:</p>
  
  <pre class="lang-js prettyprint-override"><code>$("#formchoix #checkall").click(function () {
          var tps = 0.05; //5%
          var tvq = 0.09975; //9.975%
          var subtotal = 0;
          var total = 0;
          if ($("#formchoix #checkall").is(':checked')) {
              $("#formchoix input[type=checkbox].checkchoix").each(function () {
                  //check all forms
                  $(this).prop("checked", true);
                  $(".checknom").prop("checked", true);
                  $(".checkid").prop("checked", true);
  
                  subtotal += 15; //each form is 15$
  
                  $('#subtotal').html(subtotal + '.00$'); //subtotal shown to user
  
                  var taxes = subtotal * tps * tvq;
                  total = subtotal + taxes;
                  $('#totalcost').html(total.toFixed(2) + '$'); //total shown to user
                  $('#inputTotal').val(total.toFixed(2)); //value to be sent to server
              });
  
          } else {
              $("#formchoix input[type=checkbox]").each(function () {
                  //reset everything: checkboxes, value and total shown to user
                  $(this).prop("checked", false);
                  $(".checknom").prop("checked", false);
                  $(".checkid").prop("checked", false);
  
                  subtotal = 0;
                  total = 0;
                  $('#subtotal').html('0.00$');
                  $('#totalcost').html('0.00$');
                  $('#inputTotal').val('0.00');
              });
          }
      });
  </code></pre>
  
  <p>The above code doesn't give me the right number though. For example, if my subtotal is 30$, it will show 30.15$ instead of 30.49$ like it's supposed to (based on a tax calculator online). </p>
  
  <p>I've also tried using values like 1.05 and 1.09975 and multiplicating them to the subtotal directly using <code>total = subtotal * tps * tvq</code>, but the total gave me 30.64$ (if the subtotal is 30$ like my previous example)</p>
  
  <p>Clearly what I did is wrong, so how can I make sure the total is right? </p>