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	$235.82	7.672%	$253.9121	$253.91	$253.90	$253.90
Purchase #2	$159.47	13.104%	$180.3669	$180.37	$180.35	$180.40
Purchase #3	$89.97	10.748%	$99.64	$99.64	$99.65	$99.60
Purchase #4	$179.95	5.860%	$190.4951	$190.50	$190.50	$190.50
Purchase #5	$99.76	13.733%	$113.46	$113.46	$113.45	$113.50
Purchase #6	$176.89	9.160%	$193.0931	$193.09	$193.10	$193.10
Purchase #7	$83.92	7.320%	$90.0629	$90.06	$90.05	$90.10
7 purchase totals =	$1,025.78		$1,121.0301	$1,121.03	$1,121.00	$1,121.10