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	$150.79	5.301%	$158.7834	$158.78	$158.80	$158.80
Purchase #2	$34.80	12.287%	$39.0759	$39.08	$39.10	$39.10
Purchase #3	$124.48	12.390%	$139.9031	$139.90	$139.90	$139.90
Purchase #4	$247.31	3.613%	$256.2453	$256.25	$256.25	$256.20
Purchase #5	$126.63	9.718%	$138.9359	$138.94	$138.95	$138.90
Purchase #6	$9.47	7.289%	$10.1603	$10.16	$10.15	$10.20
Purchase #7	$66.27	9.349%	$72.4656	$72.47	$72.45	$72.50
7 purchase totals =	$759.75		$815.5695	$815.58	$815.60	$815.60