Rounding means reducing the digits in a number while trying to keep it's value similar.
The result is less accurate, but easier to use.
This is the common method
* Decide which is the last digit to keep
* Increase it by 1 if the next digit is 5 or more (this is called rounding up)
* Leave it the same if the next digit is less than 5 (this is called rounding down)
Example: 243 rounded to the nearest ten is 240 (because 3 is less than 5)