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	$231.76	6.795%	$247.5081	$247.51	$247.50	$247.50
Purchase #2	$41.51	9.516%	$45.4601	$45.46	$45.45	$45.50
Purchase #3	$143.60	8.420%	$155.6911	$155.69	$155.70	$155.70
Purchase #4	$196.40	12.733%	$221.4076	$221.41	$221.40	$221.40
Purchase #5	$62.42	7.785%	$67.2794	$67.28	$67.30	$67.30
Purchase #6	$172.71	13.533%	$196.0828	$196.08	$196.10	$196.10
Purchase #7	$74.72	10.830%	$82.8122	$82.81	$82.80	$82.80
7 purchase totals =	$923.12		$1,016.2413	$1,016.24	$1,016.25	$1,016.30