The US operates exclusively under a Sales Tax system. The sales tax always appears as a separate line item, is never included in the advertised price and it (almost) always paid by the consumer to the merchant who then forwards it to the government.
Value Added Tax (VAT or GST) is a different beast. With VAT each manufacturer/distributor/retailer in the supply chain pays the government a tax based on how much they increased the value of the product and then increase the price of the product itself to recoup the cost.
Sounds to me like you are getting caught between the two systems -- no tax was collected at the various supply chain stages, so all the tax is visible at the last step, whereas in normal in-country transactions, you just see the higher "retail" price.
