Rounding to 10/100/1000 Card Game

This game allows children to practice rounding to 10/100/1000. Give each pair a sheet of cards, cut up. They should make two separate piles; one of the smaller cards and one of the larger cards. For each turn, the player turns over one small card and one large card, and completes the task, e.g.
Small card = 637
Large card = Round to the nearest 10
Answer = 640.
Replace the cards to the bottom of the piles and repeat with the other player.