Ubercart - Add store.css style sheet when viewing cart/checkout

Adds a store.css style sheet if your viewing the cart or checkout in Ubercart ecommerce.

Snippet:

<?php
//in template.php:
if (arg(0) == 'cart') drupal_add_css(drupal_get_path('theme', 'your_theme_name').'/css/store.css');
?>