$chk_products holds the total of the Product x quantity purchased, so if it is greater than 1 than more than just 1 item is being ordered ...

If you needed to check for specific items you could change it to:

Code:
$chk_products360 = 0;
$chk_products361 = 0;
$chk_products360 = $_SESSION['cart']->in_cart_check('products_id','360');
      $chk_products361 = $_SESSION['cart']->in_cart_check('products_id','361');
Then after the other products are checked, add something different for these two such as:
Code:
$chk_products += ($chk_products360 * 1.75);
$chk_products += ($chk_products361 * 2.25);
Or you can use those for any other kind of calculation ...