We have the following issue,
Unregistered users placing an order will at checkout (checkout.tpl) create an account, and fill in details.
When selecting country of residence outside of our country, tax is not updated in total due today. Naturally this can and has confused some customers.
Even though the invoice being sent out is correct, the visual feedback in checkout will still display tax.
We suggest that country selector triggers a re-calculation of total due today, so that tax can be updated.