You do not pay the tax in state you buy it. Only the state you register in. There may be some exceptions like CA and other types of taxes they levy. If you buy it and have a vin before you travel you can even save more in your own state by getting a temp regisration for the transportation from your own state. Depends on the state. If I get a vin and take it to my dmv in WY they issue a temp tranport lic then deducts that fee from permanent lic. All of my vehicles come from out of state.
Check with SD dmv and they will give you exact procedure.