I couldn't get the patch to remove all of the taxes when none applied to an order.

I finally decided it was better for the tax module to remove those line items itself. When uc_taxes_javascript() returns no taxes, getTax() will set an empty, fake line item so that the line items will be refreshed. The payment checkout pane doesn't notice this extra line item so it doesn't get displayed.

This patch has been committed to the Bazaar repository.