Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$35.26	13.857%	$40.146	$40.15	$40.15	$40.10
Purchase #2	$17.93	3.299%	$18.5215	$18.52	$18.50	$18.50
Purchase #3	$159.79	7.336%	$171.5122	$171.51	$171.50	$171.50
Purchase #4	$44.80	5.208%	$47.1332	$47.13	$47.15	$47.10
Purchase #5	$32.73	3.709%	$33.944	$33.94	$33.95	$33.90
Purchase #6	$58.49	7.379%	$62.806	$62.81	$62.80	$62.80
Purchase #7	$165.92	9.143%	$181.0901	$181.09	$181.10	$181.10
7 purchase totals =	$514.92		$555.1530	$555.15	$555.15	$555.00