If the number is five or greater you round up. Therfore if it is four or less the number is rounded down.
Now take that into consideration whilst using decimals.
To decide if you will round up or down look at the number behind the first number. If this number is a five or greater you will round the decimal up. If it id four or less you will round the decimal down.
Example: 4.25. The number behind the two after the deciaml is a five. Therefore we round this decimal down. You can round it to 4.
I hope this helps. Good Luck!