E-commerce sites in Bangladesh is VAT free by law as of now. And the tax Backpack charges is a simplified round up of complex tax calculations for products being sold in one state and traveling to another state (to the traveler). The US has different tax law based on different states and we want to make it as simple as possible for our shoppers. Rather than making the process complex for travelers and shoppers, we have made it a fixed amount to make life easier for everyone. For some cases, we pay extra for sales tax, and for some cases we don't. We prefer to keep things simple.