well, you round up if the digit behind the decimal place is 5 or more and round down if the digit is 4 or less
I guess the first is 25.64, since two decimal places means the hundredths, 3. The digit behind is 5 , meaning that 3 will become a 4.
then 315.2
then 0.398
then 15 because the digit behind 9+ is an 8 greater than 5, which means the 9 is rounded up to 10, which is a one when it passes through the decimal point, making it 15.
sorry if my explanation sucks. I hope this helps.