How do you round 652 to the nearest ten?

The two tens, on either side of 652 are 650 and 660. Which one is nearer?

652 - 650 = 2

660 - 652 = 8

So clearly 650 is nearer and that is the answer.

There is a problem when the original number ends with a 5 and both the sums give 5 as the answer. Some people believe that you should always round 5 upwards. That is wrong because it introduces an upward bias in the results. For one digit (0) you don't require rounding, for 4 of them (1,2,3,4) you round down and for 5 of them (5,6,7,8,9) you round up. So you are rounding up more often than down. That is where the bias come in.

The recommended solution to that bias is to round 5 so that the last significant digit is even.