Rounded numbers are only approximate.
An exact answer generally can not be obtained using rounded numbers. Use rounding to get a answer that is close but that does not have to be exact. How to round numbers Make the numbers that end in 1 through 4 into the next lower number that ends in 0. For example 74 rounded to the nearest ten would be 70. Numbers that end in a digit of 5 or more should be rounded up to the next even ten.