When you want to round up or down numbers focus on only two digits,which is the digit in place that you are rounding to and the digit to it's immediate right which tells you whether to round up or down.When the number you are rounding is between 0-4, you round down to the next lowest number. When the number is 5-9,you round the number up to the next highest number.
For example: If you have 25 and you want to round it up then it will be rounded up to 3 because 5 can be rounded up to the next number which is 2 to make it 3.But when you have 23,then you can't round it up which means you will have to round it down to 20 since the 3 behind the 2 can't round up.
I hope this helps......
