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	$37.87	6.592%	$40.3664	$40.37	$40.35	$40.40
Purchase #2	$37.81	12.756%	$42.633	$42.63	$42.65	$42.60
Purchase #3	$204.89	4.514%	$214.1387	$214.14	$214.15	$214.10
Purchase #4	$7.92	11.483%	$8.8295	$8.83	$8.85	$8.80
Purchase #5	$216.30	11.814%	$241.8537	$241.85	$241.85	$241.90
Purchase #6	$66.39	6.250%	$70.5394	$70.54	$70.55	$70.50
Purchase #7	$217.67	12.127%	$244.0668	$244.07	$244.05	$244.10
7 purchase totals =	$788.85		$862.4275	$862.43	$862.45	$862.40