How does POPCUSTOMS calculate the shipping cost for orders with one product?

The basic rule is:

Total product price = product price + shipping cost of the first item + shipping cost of the additional items

For example, one pair of Men's Running Shoes shipped to the United States by Standard Shipping costs $25.49.

On POPCUSTOMS, the listed product price already includes shipping to the USA, Canada, the EU, and the Rest of EU. In this example, the shipping cost included in the listed price is $0.00.