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	$38.28	10.339%	$42.2378	$42.24	$42.25	$42.20
Purchase #2	$152.29	9.748%	$167.1352	$167.14	$167.15	$167.10
Purchase #3	$44.66	4.717%	$46.7666	$46.77	$46.75	$46.80
Purchase #4	$11.72	9.430%	$12.8252	$12.83	$12.85	$12.80
Purchase #5	$140.62	10.317%	$155.1278	$155.13	$155.15	$155.10
Purchase #6	$108.32	11.507%	$120.7844	$120.78	$120.80	$120.80
Purchase #7	$203.93	10.603%	$225.5527	$225.55	$225.55	$225.60
7 purchase totals =	$699.82		$770.4297	$770.44	$770.50	$770.40