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	$246.72	12.451%	$277.4391	$277.44	$277.45	$277.40
Purchase #2	$57.86	13.739%	$65.8094	$65.81	$65.80	$65.80
Purchase #3	$72.31	13.735%	$82.2418	$82.24	$82.25	$82.20
Purchase #4	$78.90	8.464%	$85.5781	$85.58	$85.60	$85.60
Purchase #5	$138.42	5.565%	$146.1231	$146.12	$146.10	$146.10
Purchase #6	$235.37	11.580%	$262.6258	$262.63	$262.65	$262.60
Purchase #7	$12.84	11.660%	$14.3371	$14.34	$14.35	$14.30
7 purchase totals =	$842.42		$934.1544	$934.16	$934.20	$934.00