Syncing Sales Tax between Zen-Cart and PayPal's downloadable transaction records

Zen Cart works great as far as calculating state sales tax.

PayPal woks well, too, in transferring the entire total amount calculated by Zen-Cart (i.e. including tax).

The only remaining problem is that, when downloading PayPal's transaction history, it does not include any tax information.

I found on PayPal's web site some hints regarding a feature in PayPal that takes sales tax into account:

PayPal: Calculate shipping and taxes

But from reading this, it seems that if I enable sales tax in PayPal, too, then the customer will actually be charged TWICE sales tax... :eek:

I am (almost) sure that I am not the first one to face this challenge. How did you solve it? Is there a provision in Zen-Cart (and/or PayPal) to relay the sales tax information, without charging it twice?

Thanks.