Well, I solved the tax issue by modifying the paypal plugin to specify no tax in the post back to paypal (The paypal account is set to auto apply state sales tax). So for article sales, we would take the taxes out from the current sale amount manually.
Other issues with the granter user account popped up afterward, but the plugin generated different errors, so it seems the tax was it’s own issue. One solution could be to change the comparison field to compare only the pretax amount, but I suppose that would just open up a potential exploit if it was hacked (I assume a hacker could then send false communications specifying a higher tax amount).
I don’t know the exact laws on US states sales tax, but I think its based on the location of the company selling online.