Rounding whole numbers
To round, find the two tens, hundreds or thousands that your number sits between. Then pick the one it is closer to.
A worked example
Round 3 462 to the nearest hundred. It sits between 3 400 and 3 500. Look at the tens digit, the one to the right of the hundreds digit. It is 6, which is 5 or more, so 3 462 is closer to 3 500. Now round 3 462 to the nearest ten. It sits between 3 460 and 3 470. The ones digit is 2, so it is closer to 3 460. Recap: find the two neighbours, look at the next digit to the right, and 5 or more rounds up.
The mistake people actually make
A number exactly halfway between two neighbours always rounds up, so 3 465 to the nearest ten is 3 470. When you round to the nearest thousand, look at the hundreds digit, not the last digit.