Rounding to the nearest 100 Activity 5: Write the price of each of the following musical instruments to the nearest 100 dollars. Remember the rules of rounding numbers to the nearest 100; If the number that you are rounding is followed by 00, 10s, 20s, 30s, or 40s, round the number down. If the number that you are rounding is followed by 50s, 60s, 70s, 80s, or 90s, round the number up. Enjoy this rounding to the nearest 100 activity by rounding up or rounding down to the nearest 100.