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	$75.72	3.232%	$78.1673	$78.17	$78.15	$78.20
Purchase #2	$89.83	5.657%	$94.9117	$94.91	$94.90	$94.90
Purchase #3	$204.74	12.637%	$230.613	$230.61	$230.60	$230.60
Purchase #4	$154.54	13.290%	$175.0784	$175.08	$175.10	$175.10
Purchase #5	$145.92	10.685%	$161.5116	$161.51	$161.50	$161.50
Purchase #6	$89.57	10.814%	$99.2561	$99.26	$99.25	$99.30
Purchase #7	$88.28	3.169%	$91.0776	$91.08	$91.10	$91.10
7 purchase totals =	$848.60		$930.6157	$930.62	$930.60	$930.70