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	$36.99	13.151%	$41.8546	$41.85	$41.85	$41.90
Purchase #2	$146.52	3.460%	$151.5896	$151.59	$151.60	$151.60
Purchase #3	$203.93	5.171%	$214.4752	$214.48	$214.50	$214.50
Purchase #4	$154.37	10.281%	$170.2408	$170.24	$170.25	$170.20
Purchase #5	$151.69	12.805%	$171.1139	$171.11	$171.10	$171.10
Purchase #6	$37.82	7.632%	$40.7064	$40.71	$40.70	$40.70
Purchase #7	$16.51	5.579%	$17.4311	$17.43	$17.45	$17.40
7 purchase totals =	$747.83		$807.4116	$807.41	$807.45	$807.40