How can a seller charge 12.9% sales tax when no State in the union has a 12.9% sales tax?

http://community.ebay.com/t5/Auction-Listings/how-can-a-seller-charge-12-9-sales-tax-when-no-State-in-the/m-p/21480782#U21480782

Just goes to show - it's worth checking to make sure the vendor is collecting the right tax...