Rounding to the nearest hundred means replacing a number with the closest multiple of 100. Look at the tens digit: if it is 5 or more, round up; if it is 4 or fewer, round down. For example, 347 rounds to 300 and 682 rounds to 700. Rounding to hundreds is useful for estimating sums and differences of larger numbers.
Use number lines marked with hundreds to show where numbers fall. Have students name the two surrounding hundreds before deciding which is closer. Contrast with rounding to the nearest ten to solidify place-value understanding.
Rounding to the nearest hundred is the same idea as rounding to the nearest ten — just one place-value level higher. From your earlier work with rounding to tens, you learned to look at the ones digit to decide whether to round the tens digit up or down. Now, to round to the nearest hundred, you look at the tens digit to decide whether to round the hundreds digit up or down.
The rule is the same: if the digit you're examining is 5 or more, round up; if it's 4 or less, round down. For 347, the tens digit is 4 — less than 5, so round down: 347 → 300. For 682, the tens digit is 8 — 5 or more, so round up: 682 → 700. After rounding, the tens and ones digits both become 0. The number lands exactly on a multiple of 100 because that's what "nearest hundred" means.
A number line is the best tool for building intuition here. Imagine a number line with 300 and 400 marked at either end. Where does 347 sit? It's closer to 300 than to 400 (only 47 away from 300, but 53 away from 400). So it rounds to 300. For any three-digit number, you can quickly estimate its position: the tens digit tells you which half of the hundred-interval you're in. Tens digit 0–4 means you're in the lower half (closer to the lower hundred). Tens digit 5–9 means you're in the upper half (closer to the higher hundred).
The trickiest case is when the tens digit is exactly 5, like 350. That number is exactly halfway between 300 and 400. The rounding convention — round up when the digit is 5 — gives you 400. Another surprise is rounding up through a century, like 950 → 1,000. Students expect the hundreds digit to change within the same century, but 950 is closer to 1,000 than to 900, so the number crosses into four digits. This is why the number line check is always more reliable than mechanical digit-watching alone.