Rounding is a way to change a number to a simpler number that is close to the original. We often round numbers to the nearest ten, hundred, or thousand to make them easier to work with or understand.
If you have the number 27 and you want to round it to the nearest ten, you look at the ones digit. Since 7 is 5 or greater, you round up to the next ten, which is 30. If you had 23, you would round down to 20 because 3 is less than 5.