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	$217.85	13.189%	$246.5822	$246.58	$246.60	$246.60
Purchase #2	$247.81	12.157%	$277.9363	$277.94	$277.95	$277.90
Purchase #3	$154.71	7.222%	$165.8832	$165.88	$165.90	$165.90
Purchase #4	$122.51	7.377%	$131.5476	$131.55	$131.55	$131.50
Purchase #5	$54.56	3.589%	$56.5182	$56.52	$56.50	$56.50
Purchase #6	$20.71	6.773%	$22.1127	$22.11	$22.10	$22.10
Purchase #7	$175.86	13.716%	$199.981	$199.98	$200.00	$200.00
7 purchase totals =	$994.01		$1,100.5612	$1,100.56	$1,100.60	$1,100.50