We uploaded an updated page to the website yesterday that control the sales tax for checkout. Unfortunately the file didn't upload correctly so you could never actually finish the checkout process. We've corrected the problem and if you had an order you were working on refresh the Webstore/mailorder.html page and the sales tax box will appear again so you continue to check out.
We appologize for the problem. Typically we check the files after they've been uploaded but this one got past us!