if the last digit is less than 5 ,how do we round the number ? say ,for example how do we round the number 8.821?

If the last digit is less than 5, then the digit just before the last digit is retained as such and the last digit is dropped.

In 8.821, the last digit is 1(which is less than 5). So, the digit 2 is retained as such and digit 1 is dropped i.e., 8.821 is rounded to 8.82