When we round to any particular place, we look only at the single digit in the next smallest place; if that digit is 4 or less, we round down; if that digit is 5 or more, we round up.

For example, to round to the nearest hundreds, we look at the single digit in the tens place. In 647, the tens digit is 4, so we round down to the nearest hundreds, 600.

NOTE: do not double-round – first round the 47 up to 50 and then round the 650 up to 700. Double-rounding is always a mistake.