Adding to variable value on condition in Javascript

I have a variable called "total" that I would like to assign a number (or price) to and then add to that number when certain options are selected or checked. Here is the code I have so far.

Here is the code that sets the initial value (base price) of the variable that will be added to. THIS CODE CURRENTLY WORKS.

$('input[name=trimlevel]').change(function(){

      var total = 0;

      if(document.getElementById('basetrim').checked==true) {

              var total = 0;
              var basetrim = 3550.00;
              total = total + basetrim;
              $('#myTotal').html('$' + total);

      }else if(document.getElementById('upgrade').checked==true) {
                  var total = 0; 
              var upgrade = 2400.00;
              total = total + upgrade;
              $('#myTotal').html('$' + total);


       }else {
             $('#myTotal').html('$' + total);
           }


    });

Here is an example of the code used to "add to" the value of the variable. THIS IS NOT WORKING.

$('input[name=leather]').change(function(){

      if(document.getElementById('leather).checked == true) {
             var leather = 180.00;
             total = total + leather;
             $('#myTotal').html('$' + total);
      }
});

Here is the HTML for reference

<div class="modelsel">
           <h2>1. SELECT MODEL</h2> <br>
           <label for="basetrim">BASE MODEL</label> 
           <input id="basetrim" type="radio" name="trimlevel" value="2400.00">
           <label for="upgrade">UPGRADED MODEL</label> 
           <input id="upgrade" type="radio" name="trimlevel" value="3550.00">

 </div>

<div class="inside">
          <h2>3. BASE MODEL ADD-ONS</h2><br>
          <input type="checkbox" value="180.00" id="leather" name="leather" />
           <label for="leather">Leather Seat (+ $180.00)</label><br>
</div>

<div id="myTotal"></div>

I am relatively new to Javascript and have been struggling with this for hours. Any help is appreciated. Thanks in advance.