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	$10.89	5.807%	$11.5224	$11.52	$11.50	$11.50
Purchase #2	$174.52	11.816%	$195.1413	$195.14	$195.15	$195.10
Purchase #3	$186.89	13.697%	$212.4883	$212.49	$212.50	$212.50
Purchase #4	$8.93	9.430%	$9.7721	$9.77	$9.75	$9.80
Purchase #5	$146.41	3.345%	$151.3074	$151.31	$151.30	$151.30
Purchase #6	$93.94	4.820%	$98.4679	$98.47	$98.45	$98.50
Purchase #7	$19.51	6.672%	$20.8117	$20.81	$20.80	$20.80
7 purchase totals =	$641.09		$699.5111	$699.51	$699.45	$699.50