You have in your wallet, and you want to buy new skiing equipment for and some ski wax for . Do you have enough money to buy both?
$ becomes $ after rounding, and $ becomes $ after rounding.
According to the estimate, you should have enough money to buy both the skiing equipment and the ski wax. But if you calculate how much they’re actually going to cost, you get
which actually means you would not have enough money for both the skiing equipment and the ski wax. This is the reason it’s better to round up rather than down when you are shopping.