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	$37.30	8.730%	$40.5563	$40.56	$40.55	$40.60
Purchase #2	$120.42	4.338%	$125.6438	$125.64	$125.65	$125.60
Purchase #3	$204.52	6.208%	$217.2166	$217.22	$217.20	$217.20
Purchase #4	$77.66	3.561%	$80.4255	$80.43	$80.45	$80.40
Purchase #5	$111.51	6.286%	$118.5195	$118.52	$118.50	$118.50
Purchase #6	$9.84	11.567%	$10.9782	$10.98	$11.00	$11.00
Purchase #7	$48.91	8.595%	$53.1138	$53.11	$53.10	$53.10
7 purchase totals =	$610.16		$646.4537	$646.46	$646.45	$646.40