After adding a tax modifier to the mix I am no longer able to connect with the PayPal Payment Gateway. The debug.log states that:
“[L_SHORTMESSAGE0] => Transaction refused because of an invalid argument. See additional error messages for details.
[L_LONGMESSAGE0] => Order total is invalid. “
This may be to do with the cents value not being rounded to 2 decimal places.
I've also uncovered another issue: #65
Closing, because this a payment module issue, not shop.