First get the right number of the digit that is rounded off
example: 0.123 rounded to the nearest hundredths
so,you get the right number of the hundredths digit
example:0.123 get the right of  the hundredths digit. the right digit is 3
second if the digit is lower than 4,copy the remaining decimals.
if the digit is greater than 5,add 1 to the digit you rounding off
example:0.123 = 0.12
other examples
0.157 rounded to the nearest tenths = 0.2
0.5545 rounded to the nearest thousandths = 0.555
you get it?
bye that's all!