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	$28.50	13.486%	$32.3435	$32.34	$32.35	$32.30
Purchase #2	$120.52	5.468%	$127.11	$127.11	$127.10	$127.10
Purchase #3	$49.90	13.730%	$56.7513	$56.75	$56.75	$56.80
Purchase #4	$164.58	12.108%	$184.5073	$184.51	$184.50	$184.50
Purchase #5	$158.67	3.123%	$163.6253	$163.63	$163.65	$163.60
Purchase #6	$95.72	9.734%	$105.0374	$105.04	$105.05	$105.00
Purchase #7	$21.46	3.242%	$22.1557	$22.16	$22.15	$22.20
7 purchase totals =	$639.35		$691.5305	$691.54	$691.55	$691.50