Amazon collects sales tax here in Texas and it hasn't changed my buying habits at all as far as I can tell.
Note: I'm also a Texan who hasn't decreased his Amazon spend since sales tax started, if anything I've increased my Amazon spend over the last few quarters.
This way they can build local fulfillment centers (which force them to collect sales tax), and yet not actually have to charge it.
It doesn't work for every item, but it does for quite a few of them.