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	$63.43	13.733%	$72.1408	$72.14	$72.15	$72.10
Purchase #2	$139.25	7.592%	$149.8219	$149.82	$149.80	$149.80
Purchase #3	$138.49	11.559%	$154.4981	$154.50	$154.50	$154.50
Purchase #4	$37.32	6.145%	$39.6133	$39.61	$39.60	$39.60
Purchase #5	$39.27	13.317%	$44.4996	$44.50	$44.50	$44.50
Purchase #6	$5.93	4.435%	$6.193	$6.19	$6.20	$6.20
Purchase #7	$54.65	3.400%	$56.5081	$56.51	$56.50	$56.50
7 purchase totals =	$478.34		$523.2748	$523.27	$523.25	$523.20