Sales taxes are levied under the laws of the state where the sale occurs.
The state requires the seller to charge the tax, and as the sale occurs at the sellers location, the tax is due regardless of where the buyer resides.
Depending on the state, and its laws, sales taxes are waived on a sale of an item which will be resold by the buyer, IF the buyer has a sales tax permit and will be collecting and paying sales tax proceeds to a state taxing authority.
This is my experience. I have lived in Oregon the majority of my life, with some time in Alaska, Washington, Texas, Illinois, and Virginia. The ONLY state I have ever had sales tax waived was in stores in Washington. If you are buying a non-consumable product, like a TV, CD, clothing, or such, you can show your Oregon ID without paying tax. If you eat there (restaurant) or have a service done, you pay tax, whether you live there or not. When I lived in other states, like Alaska and Illinois, I let it be known I was from out of state, but I always had to pay sales tax. So given this, if you are in a store outside Oregon, not counting the Washington exception, you will more than likely pay sales tax. It never hurts ask for a waiver, but they don't have to.