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	$15.62	9.422%	$17.0917	$17.09	$17.10	$17.10
Purchase #2	$40.39	5.265%	$42.5165	$42.52	$42.50	$42.50
Purchase #3	$20.25	12.263%	$22.7333	$22.73	$22.75	$22.70
Purchase #4	$90.75	10.815%	$100.5646	$100.56	$100.55	$100.60
Purchase #5	$166.95	10.583%	$184.6183	$184.62	$184.60	$184.60
Purchase #6	$227.95	9.850%	$250.4031	$250.40	$250.40	$250.40
Purchase #7	$118.34	6.620%	$126.1741	$126.17	$126.15	$126.20
7 purchase totals =	$680.25		$744.1016	$744.09	$744.05	$744.10