My totals are wrong after a currency or tax change, can you fix the calculation?

Yes. Wrong totals after switching currency or changing a tax class are usually rounding drift, a stale exchange rate, or a tax rule applied to the wrong geo zone. We trace the calculation through system/library/cart and the tax classes, reconcile the math against expected totals, and confirm the cart, checkout and order confirmation all show the same figure across every currency you sell in.