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	$129.70	12.685%	$146.1524	$146.15	$146.15	$146.20
Purchase #2	$11.81	6.486%	$12.576	$12.58	$12.60	$12.60
Purchase #3	$29.42	7.268%	$31.5582	$31.56	$31.55	$31.60
Purchase #4	$7.25	3.786%	$7.5245	$7.52	$7.50	$7.50
Purchase #5	$104.40	6.571%	$111.2601	$111.26	$111.25	$111.30
Purchase #6	$182.41	13.387%	$206.8292	$206.83	$206.85	$206.80
Purchase #7	$119.95	8.587%	$130.2501	$130.25	$130.25	$130.30
7 purchase totals =	$584.94		$646.1505	$646.15	$646.15	$646.30