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	$24.68	3.335%	$25.5031	$25.50	$25.50	$25.50
Purchase #2	$107.71	10.203%	$118.6997	$118.70	$118.70	$118.70
Purchase #3	$138.75	4.426%	$144.8911	$144.89	$144.90	$144.90
Purchase #4	$9.47	8.104%	$10.2374	$10.24	$10.25	$10.20
Purchase #5	$139.41	8.733%	$151.5847	$151.58	$151.60	$151.60
Purchase #6	$43.65	5.157%	$45.901	$45.90	$45.90	$45.90
Purchase #7	$91.66	13.149%	$103.7124	$103.71	$103.70	$103.70
7 purchase totals =	$555.33		$600.5294	$600.52	$600.55	$600.50