Rounding numbers to the nearest $10 makes doing any kind of money math much easier to calculate. This happens because rounding numbers turns them into whole numbers, and whole numbers are easier to work with. Whenever you have a number that ends in 1, 2, 3 or 4, that number will be rounded down to the nearest 10. For example, 12 rounds down to 10 and 24 will round down to 20. Any number ending in 5, 6, 7, 8 or 9 will be rounded up.

Lay out the money on the table. This will make it easier to separate the money for counting to find out the number which must be rounded.

Round the number up to the nearest $10 amount (10, 20, 30, 40) if the total that was counted ends in 5 or more. For example, if the total is $46, it will be rounded up to $50. Rounding up is good for finding out high estimate of money totals.

Round the total money down if the total number ends in 4 or less. This helps to give low estimates on monetary totals.
Tips & Warnings
 Rounding up is a great tool for figuring the maximum amount of something and rounding down is good for finding a minimum.
 Bear in mind that the rounded totals are approximate.
References
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