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	$142.51	12.702%	$160.6116	$160.61	$160.60	$160.60
Purchase #2	$74.84	11.852%	$83.71	$83.71	$83.70	$83.70
Purchase #3	$243.36	5.415%	$256.5379	$256.54	$256.55	$256.50
Purchase #4	$226.40	10.372%	$249.8822	$249.88	$249.90	$249.90
Purchase #5	$200.70	6.726%	$214.1991	$214.20	$214.20	$214.20
Purchase #6	$78.52	13.733%	$89.3032	$89.30	$89.30	$89.30
Purchase #7	$137.85	6.211%	$146.4119	$146.41	$146.40	$146.40
7 purchase totals =	$1,104.18		$1,200.6559	$1,200.65	$1,200.65	$1,200.60