State the rig is licensed in.
Some states like Washington where I am. IF you pay the tax in SC, then when you register here, if the tax is lower there than here, in this case, more than likely, as it is 9.x% here......you pay the difference from that state to here. OR if by some chance the tax is higher, you get a refund.
Will not say how it will work in your case. but that is how it works here any how!
marty