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	$37.72	13.201%	$42.6994	$42.70	$42.70	$42.70
Purchase #2	$44.60	13.124%	$50.4533	$50.45	$50.45	$50.50
Purchase #3	$83.77	12.827%	$94.5152	$94.52	$94.50	$94.50
Purchase #4	$179.59	10.187%	$197.8848	$197.88	$197.90	$197.90
Purchase #5	$99.52	5.429%	$104.9229	$104.92	$104.90	$104.90
Purchase #6	$31.90	5.777%	$33.7429	$33.74	$33.75	$33.70
Purchase #7	$20.44	3.314%	$21.1174	$21.12	$21.10	$21.10
7 purchase totals =	$497.54		$545.3359	$545.33	$545.30	$545.30