The Shopkeeper's Method

Before calculators, cashiers never subtracted to make change. They counted up from the price to the cash you handed over.

Buy a $7.35 item and pay with a $20 bill. The cashier counts: "$7.35, plus 5 cents makes $7.40, plus 60 cents makes $8, plus $2 makes $10, plus $10 makes $20." Your change is $12.65, found with only addition.

It feels easier because adding forward is friendlier than borrowing across a row of zeros.