I am trying to add shipping prices to my product. I have a paypal "add to cart" button setup on my website. The product sells for 10.00 for each item, with $4.00 shipping per item. If someone were to order two items, then it would be $20.00 plus $8.00 for shipping and so one. However, when I try to order more than one item the shipping price stays at $4.00 no matter how many items I want to buy. Is there a way to set this up correctly?