Sherri should round the estimate of gratuity of the restaurant server to 20% in order to get a good estimate.
In order to round off the gratuity of the restaurant server, which is 18% to a good estimate, we would be rounding off to the nearest ten. Because the unit digit is greater than 5, 1 would be added to the tens digit while the units digit would become 0. 18% becomes 20%.
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