Как через ajax запрос отдается 3 параметра $('#button-cart').on('click', function() {

$.ajax({
url: 'index.php?route=checkout/cart/add',
type: 'post',
data: $('#product input[type=\'text\'], #product input[type=\'hidden\'], #product input[type=\'radio\']:checked, #product input[type=\'checkbox\']:checked, #product select, #product textarea'),
dataType: 'json',
beforeSend: function() {
/*$('#button-cart').button('loading');*/
},
complete: function() {
/*$('#button-cart').button('reset');*/
},
success: function(json) {
$('.alert, .text-danger').remove();
$('.form-group').removeClass('has-error');

if (json['error']) {
if (json['error']['option']) {
for (i in json['error']['option']) {
var element = $('#input-option' + i.replace('_', '-'));

if (element.parent().hasClass('input-group')) {
element.parent().after('<div class="text-danger">' + json['error']['option'][i] + '</div>');
} else {
element.after('<div class="text-danger">' + json['error']['option'][i] + '</div>');
}
}
}

if (json['error']['recurring']) {
$('select[name=\'recurring_id\']').after('<div class="text-danger">' + json['error']['recurring'] + '</div>');
}

// Highlight any found errors
$('.text-danger').parent().addClass('has-error');
}

if (json['success']) {
/*$('.breadcrumb').after('<div class="alert alert-success">' + json['success'] + '<button type="button" class="close" data-dismiss="alert">&times;</button></div>');*/

$('#cart .basket').html('<span id="cart-total"> ' + json['total'] + '</span>');

//$('html, body').animate({ scrollTop: 0 }, 'slow');
$('.cart-popup-open').click();
$('.pop-added_t').text(json['name']);

$('#cart .basket-hover > ul').load('index.php?route=common/cart/info ul li');
}
},
error: function(xhr, ajaxOptions, thrownError) {
alert(thrownError + "\r\n" + xhr.statusText + "\r\n" + xhr.responseText);
}
});
});

я так понимаю ты корзину хочешь кастомизировать?