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	$36.70	12.185%	$41.1719	$41.17	$41.15	$41.20
Purchase #2	$207.69	3.239%	$214.4171	$214.42	$214.40	$214.40
Purchase #3	$160.28	13.253%	$181.5219	$181.52	$181.50	$181.50
Purchase #4	$239.28	6.452%	$254.7183	$254.72	$254.70	$254.70
Purchase #5	$89.90	11.648%	$100.3716	$100.37	$100.35	$100.40
Purchase #6	$243.61	5.222%	$256.3313	$256.33	$256.35	$256.30
Purchase #7	$227.72	12.605%	$256.4241	$256.42	$256.40	$256.40
7 purchase totals =	$1,205.18		$1,304.9562	$1,304.95	$1,304.85	$1,304.90