bendthearccheckbox.js

$(document).ready( function() {
  $.fn.extend({
    toggleCheck: function (isChecked) {
      var $element = $(this);
      $element.find('input').prop('checked', isChecked);
      $element.toggleClass('selected', isChecked);
    }
  });

  var $containers = $('span.donation_amount_option_container'),
      $checkedInput = $containers.find('input:checked'),
      hasValue = $checkedInput.length,
      defaultValue = 50;

  $containers.each( function () {
    var $container = $(this),
        $input = $container.find('input'),
        isChecked = $input.is($checkedInput),
        value = $input.val(),
        valueClass = 'donate-' + value,
        isDefault = value == defaultValue;

    $container.addClass(valueClass);

    if (hasValue) {
      $container.toggleClass('selected', isChecked);
    }
    else {
      $container.toggleCheck(isDefault);
    }
  });

  $containers.click( function () {
    var clicked = this;

    $containers.each( function () {
      var $container = $(this),
          isClicked = $container.is(clicked);

      $container.toggleCheck(isClicked);
    });
  });
});