Explain the idea of rounding numbers while demonstrating on a white board or chalkboard. Take a moment to review place value, using such terms as "ones," "tens" and "hundreds." Tell students that to round is to make the number easier to work with, but less accurate. The first step in rounding is to decide which is the last digit to keep, or stay the same. For example, if rounding 793 to the nearest 10, then 9 would be the last digit to "keep." Students should underline the 9, since that is the digit in the place they are rounding to. The underlined digit will stay the same
if the next digit is less than 5 (this is called rounding down) and increase by 1 if the next digit is 5 or greater (this is called rounding up). When students underline the digit in the place they are rounding to, they should then draw an arrow to the digit immediately to the right, since that is the digit that they will look at to determine if they should round up or down.
Have students pretend they are shopping in a store. Create prices for the play items (just simple things that can be found around the classroom) that end in odd numbers, such as $1.47. Use stickers or adhesive paper to label prices on a few dozen items. Have students estimate the total cost of the items they choose by rounding the prices. For example, have them choose 10 items to "buy." Then they should estimate the total cost by rounding. At first have them round to the nearest dollar. So if they choose an item that is $1.47, they would round to $1, if they choose an item that is $2.58, they will round to $3. Have them trade price lists with a partner to check if they rounded the prices correctly.
Give students a long list of three-digit numbers to add. Each time you read out a number, have them quickly round it up or down, by rounding to the nearest hundred. So for example if you say "938," they would write "900." If you say "489," they would write "500." Read the numbers quickly, so they practice rounding with quick, decisive changes. At the end, have students reveal their totals and compare them with other students in the class.
Play a simple memory game by making cards with two- and three-digit numbers and with assorted two- and three-digit numbers rounded to the nearest 10 and hundred. Create pairs to set up, where a pair consists of a number and the number it would round to after rounding to a certain place value; for example 53 and 50. Students turn the cards face down in rows,and flip over cards two at a time, creating "matches" by pairing the number with the number it would round to.