Enumerate the Rules in rounding off the numbers?

Answer 1

Suppose you need to round to n digits.

Look at the (n+1)th digit.

If it is 0 you do not need to round. You simply delete all digits after the nth.

If it is 1, 2, 3 or 4 you again delete all digits after it.

If it is 6, 7, 8 or 9 you increase the nth digit by 1 and delete all subsequent digits.

If it is 5, then

if n is even you delete all subsequent digits,

if the nth digit is odd you add one and delete all subsequent digits.

Statistically naive people recommend that 5 is always rounded up without realising that this introduced an upward bias.

Answer 2

Look to the right of the digit you are rounding.

If the next digit (and all that follow) is 0, there is no issue.

If the next digit is 1, 2, 3 or 4 then ignore them.

If the next digit is 6, 7, 8, or 9 then add one to the digit that you are rounding.

If the next digit is 5 you can go either way. So as not to introduce a bias, you should round up half the time and round dwon half the time. The conventional solution, used by many statisticians, is to round up or down so that the previous digit is (or becomes) even.