You better be careful if using your credit card statement amounts. For example, what if you go to a restaurant, the bill is $40, you tip $10, your credit card statement will show $50. Only $40 worth was taxed, though. Same with grocery stores - most food isn't even taxed, so you can't use the total amount from your credit card. Some online purchases don't charge tax, just a flat amount. To be safe, most drive thrus, home goods, hardware, furniture, etc... you can use the whole amount.
