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	$170.42	12.278%	$191.3442	$191.34	$191.35	$191.30
Purchase #2	$229.42	8.164%	$248.1498	$248.15	$248.15	$248.10
Purchase #3	$155.52	11.606%	$173.5697	$173.57	$173.55	$173.60
Purchase #4	$25.83	9.130%	$28.1883	$28.19	$28.20	$28.20
Purchase #5	$61.68	3.172%	$63.6365	$63.64	$63.65	$63.60
Purchase #6	$99.86	11.628%	$111.4717	$111.47	$111.45	$111.50
Purchase #7	$90.95	13.733%	$103.4402	$103.44	$103.45	$103.40
7 purchase totals =	$833.68		$919.8004	$919.80	$919.80	$919.70