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	$125.66	6.236%	$133.4962	$133.50	$133.50	$133.50
Purchase #2	$122.37	12.650%	$137.8498	$137.85	$137.85	$137.80
Purchase #3	$211.52	6.390%	$225.0361	$225.04	$225.05	$225.00
Purchase #4	$6.71	7.560%	$7.2173	$7.22	$7.20	$7.20
Purchase #5	$83.34	7.560%	$89.6405	$89.64	$89.65	$89.60
Purchase #6	$100.28	11.603%	$111.9155	$111.92	$111.90	$111.90
Purchase #7	$86.58	3.837%	$89.9021	$89.90	$89.90	$89.90
7 purchase totals =	$736.46		$795.0575	$795.07	$795.05	$794.90