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	$26.40	6.668%	$28.1604	$28.16	$28.15	$28.20
Purchase #2	$117.86	4.414%	$123.0623	$123.06	$123.05	$123.10
Purchase #3	$114.87	3.811%	$119.2477	$119.25	$119.25	$119.20
Purchase #4	$100.30	11.496%	$111.8305	$111.83	$111.85	$111.80
Purchase #5	$191.49	8.793%	$208.3277	$208.33	$208.35	$208.30
Purchase #6	$205.81	5.856%	$217.8622	$217.86	$217.85	$217.90
Purchase #7	$132.72	6.189%	$140.934	$140.93	$140.95	$140.90
7 purchase totals =	$889.45		$949.4248	$949.42	$949.45	$949.40