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	$80.97	12.486%	$91.0799	$91.08	$91.10	$91.10
Purchase #2	$99.61	4.803%	$104.3943	$104.39	$104.40	$104.40
Purchase #3	$244.72	13.810%	$278.5158	$278.52	$278.50	$278.50
Purchase #4	$105.86	5.748%	$111.9448	$111.94	$111.95	$111.90
Purchase #5	$69.86	3.313%	$72.1745	$72.17	$72.15	$72.20
Purchase #6	$161.82	8.698%	$175.8951	$175.90	$175.90	$175.90
Purchase #7	$145.70	8.485%	$158.0626	$158.06	$158.05	$158.10
7 purchase totals =	$908.54		$992.0670	$992.06	$992.05	$992.10