In the United States, gasoline prices are usually written with the decimal part as thousandths of a dollar. For example, a gas station might post the price of unleaded gas at $\$3.279$ per gallon. But if you were to buy exactly one gallon of gas at this price, you would pay $$3.28$ , because the final price would be rounded to the nearest cent. In a lesson about whole numbers, we learned that we can round numbers to get an approximate value when the exact value is not needed.

Suppose we wanted to round $$2.72$ to the nearest dollar. Is it closer to $$2$ or to $$3$? What if we wanted to round $$2.72$ to the nearest ten cents; is it closer to $$2.70$ or to $$2.80$? The number lines in the image below can help us answer those questions.

(a) We see that $2.72$ is closer to $3$ than to $2$. So, $2.72$ rounded to the nearest whole number is $3$.

(b) We see that $2.72$ is closer to $2.70$ than $2.80$. So we say that $2.72$ rounded to the nearest tenth is $2.7$.

Can we round decimals without number lines? Yes! We use a method based on the one we used to round whole numbers.

 

Tip:  If the digit to the right of your given place value is 5 or above, give your given place value a shove.  If the digit to the right of your given place value is 4 or less, let your given place value rest.