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	$157.66	7.141%	$168.9185	$168.92	$168.90	$168.90
Purchase #2	$181.82	11.145%	$202.0838	$202.08	$202.10	$202.10
Purchase #3	$38.30	13.454%	$43.4529	$43.45	$43.45	$43.50
Purchase #4	$29.91	8.698%	$32.5116	$32.51	$32.50	$32.50
Purchase #5	$121.62	7.581%	$130.84	$130.84	$130.85	$130.80
Purchase #6	$121.43	13.152%	$137.4005	$137.40	$137.40	$137.40
Purchase #7	$85.51	4.748%	$89.57	$89.57	$89.55	$89.60
7 purchase totals =	$736.25		$804.7773	$804.77	$804.75	$804.80