To round a number to the nearest hundreds, you will need to check the number in the tens position:
(1) If the number in the tens position is less that 5, then, all you will do is convert the tens and units of the original number to zeros and that's it.
(2) If the number in the tens position is 5 or more, then you will add one to the hundreds and then convert the tens and units to zeros.
Taking a look at the number we have (12,000), we will find that the number in the hundreds position is a zero, which means that the second case is invalid here.
This means that, the number might be any number whose tens is less than 5.
Examples:
12,010
12,019
12,045
12,049
12,022