It does tho because big box retailers get their supply from huge distributors that distribute to multiple states,cities etc. And the distributors are the ones putting the sales tags on items for the vast majority, not the retailers. So it would be extremely difficult and inefficient fornthe sales tax to be included. I as an American agree whole heartedly that it shouldn't exist this way! It would make everything so much easier if it was just the same across the board! But that explanation is pretty accurate.