When rounding decimals to the nearest whole one the only digits that are crucial are the tenths – it does not matter what the hundredths or thousandths are.
When rounding a number such as 3.47 to the nearest whole number the key digit to look at is the tenths digit. If it is 5 or more, round up. Less than 5, round down.
So 3.44 rounded to the nearest whole one is 3.
3.47 rounded to the nearest whole one is 4.