AFAIK tax on out of state purchase is illegal. Because of that my state (Illinois) collects "use tax" - different name of the same thing. Since I don't remember what I bought where I use option of paying fixed "use tax" proportional to gross income. I found this:
"What Are Use Taxes
As a general rule, a state's taxing power reaches only as far as its borders. What this means for sales tax purposes is that a state cannot impose its sales tax on retail sales that are consummated in other states. Because states can tax only transactions within their borders, there is a big loophole from the perspective of the State Department of Revenue. A state's residents could avoid paying a state's sales tax by making their purchases outside the state, either by crossing the border to an adjoining state or by making purchases via the Internet. To close this loophole, each state that has a sales tax also has a complementary "use" tax. The use tax applies to the "use, storage, or other consumption" within the state of tangible personal property, the purchase of which would have been subject to the sales tax had the transaction occurred within the state."
"What Are Use Taxes
As a general rule, a state's taxing power reaches only as far as its borders. What this means for sales tax purposes is that a state cannot impose its sales tax on retail sales that are consummated in other states. Because states can tax only transactions within their borders, there is a big loophole from the perspective of the State Department of Revenue. A state's residents could avoid paying a state's sales tax by making their purchases outside the state, either by crossing the border to an adjoining state or by making purchases via the Internet. To close this loophole, each state that has a sales tax also has a complementary "use" tax. The use tax applies to the "use, storage, or other consumption" within the state of tangible personal property, the purchase of which would have been subject to the sales tax had the transaction occurred within the state."