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	$17.65	12.223%	$19.8074	$19.81	$19.80	$19.80
Purchase #2	$174.87	11.733%	$195.3875	$195.39	$195.40	$195.40
Purchase #3	$123.45	11.810%	$138.0294	$138.03	$138.05	$138.00
Purchase #4	$34.58	8.468%	$37.5082	$37.51	$37.50	$37.50
Purchase #5	$200.60	11.341%	$223.35	$223.35	$223.35	$223.40
Purchase #6	$87.66	13.811%	$99.7667	$99.77	$99.75	$99.80
Purchase #7	$148.33	5.537%	$156.543	$156.54	$156.55	$156.50
7 purchase totals =	$787.14		$870.3922	$870.40	$870.40	$870.40