It seems that when a user is not logged in and the system doesn't yet know the bill address - it adds the tax rates for every province and country. It needs a way to specify a default tax rate that can be over ridden when the user specifies a bill to address.
yes, please look in bug forum first, http://forum.virtuemart.net/index.php?topic=92144.0
just fixed today, but thanks for notifying us.