While there can be a number of different solutions to this question, there are a couple of primary possibilities we suggest looking into first:
Very likely. 1) Your POS system likely takes a discount from the grand total. It's less confusing for customers when they receive a discount, but technically it's not correct. Our discounts are always taken from the subtotal and then we calculate tax. Ultimately, customers should not be taxed on an amount they did not pay.
Less likely. 2) Your tax rate was incorrectly set in either your POS or our system. Check it under restaurant settings>restaurant settings.