Help your child memorize this poem:
"Find you number,
Look right next door,
4 or less, just ignore,
5 or more, add one more."
Keep a written copy of the poem handy for use when doing rounding math homework. Some kids like to tape it to their math book, or put it in their school agenda, or post it on the fridge, or keep it somewhere by their study area.
Explain the first line of the poem, "Find you number." When you are rounding a number, you round to a specific place value: "Round this number to nearest hundreds place."
Have your child prove that he knows which place his is rounding to by underlining that place in the digits. If the child were given the number 245,768 he should underline the 7 because it's in the hundreds place.
Explain the second phrase, "Look right next door." Have your child draw an arrow to the digit immediately to the right of the underlined number which, in the example 245,768 would be 6. Explain that this is the neighbor next door, and that it is very bossy! It can push the underlined number around sometimes. If it's big enough, that neighbor number can push the digit next to it right up to being a bigger number. But if the neighbor number isn't big enough, the digit next to it remains the same. It's the neighbor number that decides if the underlined digit changes or remains the same.
Explain the next line, "4 or less, just ignore." If the neighbor with the arrow pointing to it is 4 or less, then the digit in question will stay the same. The neighbor number isn't big enough to push the digit to be bigger. All the neighbor numbers to the right then become zeros. Stress to your child that rounding always results in numbers ending with one or more zeros.
Explain the last phrase, "5 or more, add one more." If the neighbor number is 5 or greater, it's big enough to push the underlined digit into a bigger number. Tell your child to change that number, leaving the rest of the neighbors to the left as they are, and all the ones to the right are changed to zeros.