Rounding Money Cheat Sheet for Middle & High School Math

"Wait, does $45.678 round to $45.67 or $45.68?" 

Your high school students are in the middle of solving compound interest problems, and suddenly you overhear an elementary skill rearing its ugly head-- rounding. Why is rounding money to the hundredths place such a sticking point for students, even older students in middle and high school? 

Why is Rounding Money So Hard? 

If your students struggle with rounding like mine have, there may be a few reasons: 

• Longer is Larger: Students see more numbers and think bigger value. $45.678 has more numbers than $45.68, so $45.678 must be a bigger number, right? 

• The rule without the reason: Many students memorize some variation of "5 or above, give it a shove" without ever understanding proximity. They don't see that $0.678 is physically closer to $0.68 than $0.67 on a number line. They just see a string of digits. 

• Place Value Disconnect: We rarely use physical pennies anymore, or cash in general. Lack of practice with real coins has added to the disconnect between cents and the hundredths place. 

Where does rounding money come up in the real world? 

We don't often see rounding money in the real world with credit cards, debit cards, and cash registers dominating over cash transactions, but they happen millions of times a day.

The Gas Station 9/10: If you look at any gas station sign, the price isn’t just $3.45, it’s $3.459. That tiny 9 at the end is 9/10ths of a cent, which seems like nothing. But $3.46 is 9x closer to $3.459 than $3.45 is to $3.459! So it really matters! 


Sales Tax Calculations: Here in Massachusetts, sales tax is 6.25%, making money amounts into the thousandths and beyond very common. Cash registers usually do all of the calculations for us, but students should know what is happening “behind the scenes”. 

Buying a $18.99 calculator at 6.25% sales tax results in a total cost of $20.176875, requiring rounding. Stores will round this amount to $20.18 and keep the fractional penny. 

Interest on Savings and Loans: Fractional pennies are common when calculating compound interest. If a student has $500.25 in an account earning 4.3% annually, the daily interest earned is $0.0589335617. The bank doesn't just ignore those decimals, they round to the nearest cent ($0.06). 

With millions of customers, rounding correctly means the difference between a bank being profitable or losing a fortune. Office Space, anyone? 

Unit Pricing at the Grocery Store: To compare a 12oz box of cereal to a Family Size 20oz box, you have to divide the price by the weight. A box of cereal that costs $5.49 for 18oz is $0.305 per ounce. To make it readable for the consumer, the store often rounds this to $0.31 per oz. on the tag. Knowing how to round helps a shopper decide if the Family Size is actually a better deal.

To help support students learning to round money, or working on practice problems where they have to round money (and may not be 100% confident), I made this rounding money cheat sheet reference for student notebooks. It's a 1/2 sheet that supports students rounding money to the nearest cent.

> Browse more consumer math resources

More rounding resources

3rd grade rounding references

These rounding numbers references are part of a 3rd grade math word wall.

5th grade place value

A firm grasp of place value helps when developing rounding skills. This place value reference is in my blog's free math resource library, and is part of a large 5th grade math word wall.

More "sticky" math topics:

Integers

Fractions

Slope