When you file your state business taxes, you put down how much state sales tax you paid, and then you get it back as a credit (not a deduction), so you basically get it all back at the end of the year, if you have a resellers license.

Also, some retailers let you file your resellers license with them and then they don't charge you sales tax because they know you are a vendor who is going to resell it. This system is often abused by small businesses who buy personal items along with their business items and then don't pay tax on their personal items. In theory they have to file use tax at the end of the year (the same use tax you're supposed to file if you buy something out of state and aren't taxed on it), but most people don't.