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	$205.26	12.247%	$230.3982	$230.40	$230.40	$230.40
Purchase #2	$177.77	12.169%	$199.4028	$199.40	$199.40	$199.40
Purchase #3	$145.33	6.543%	$154.8389	$154.84	$154.85	$154.80
Purchase #4	$240.78	6.353%	$256.0768	$256.08	$256.10	$256.10
Purchase #5	$181.90	13.155%	$205.8289	$205.83	$205.85	$205.80
Purchase #6	$49.72	6.179%	$52.7922	$52.79	$52.80	$52.80
Purchase #7	$120.83	5.590%	$127.5844	$127.58	$127.60	$127.60
7 purchase totals =	$1,121.59		$1,226.9222	$1,226.92	$1,227.00	$1,226.90