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	$83.87	8.658%	$91.1315	$91.13	$91.15	$91.10
Purchase #2	$12.72	11.204%	$14.1451	$14.15	$14.15	$14.10
Purchase #3	$100.49	4.793%	$105.3065	$105.31	$105.30	$105.30
Purchase #4	$190.71	12.283%	$214.1349	$214.13	$214.15	$214.10
Purchase #5	$22.90	13.651%	$26.0261	$26.03	$26.05	$26.00
Purchase #6	$175.71	9.191%	$191.8595	$191.86	$191.85	$191.90
Purchase #7	$135.61	13.773%	$154.2876	$154.29	$154.30	$154.30
7 purchase totals =	$722.01		$796.8912	$796.90	$796.95	$796.80