<ul id="myTab" class="nav nav-tabs">
    <li class="reports active left"><a href="#home" data-toggle="tab" >Details</a></li>
    <li class="reports right not_active" ><a href="#profile" data-toggle="tab" >Analytics</a></li>
  </ul>

$('#myTab a:last').tab('show');

$("#my-form-id").submit(function () {
    $.ajax({
      url: "my-form-handler.php",
      type: "POST",
      data: $("#my-form-id").serialize(),
      success: function(data) {
        $('#myTab a:last').tab('show');
      }
    });
    return false;
});