[Hectic]

I think technically you should only have to pay the taxes that are inforced within your provence.
That being said it is probably easyer (accounting wise) for retailers to just collect taxes as required in their provence also itll help them avoid funny looks from from the cra come tax time.
I know in the states they have this all worked out and if you are in a state that charges certian taxes you will pay them upon check out. Here in canada its not really standardized or inforced in that way so retailers baisically sell stuff as if you are walking into their storefront and buying it (again just making it easyer on themselves as far as bookkeeping and tax filing is concerned)
Im sure that wasnt any real help but i think this is what your experiencing and why lol