one-time customer in b2c scenario with tax jurisdiction code

We'd like to implement a web application for b2c. All orders will be stored in SAP using the address override (so we don't have to create customer masters). This triggers for each address the tax jurisdiction code determination (external in our case), which may find no or multiple tax jurisdiction codes.

The standard b2c user has no idea what a tax jurisdiction code is, therefore we cannot give him the options. But we cannot just block the tax jurisdiction code determination, because we have to know the taxes for charging the user's credit card with the right amount.

How are other projects handling this ?