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	$38.99	4.350%	$40.6861	$40.69	$40.70	$40.70
Purchase #2	$153.52	5.418%	$161.8377	$161.84	$161.85	$161.80
Purchase #3	$10.57	5.171%	$11.1166	$11.12	$11.10	$11.10
Purchase #4	$138.58	5.548%	$146.2684	$146.27	$146.25	$146.30
Purchase #5	$118.27	10.816%	$131.0621	$131.06	$131.05	$131.10
Purchase #6	$66.63	9.385%	$72.8832	$72.88	$72.90	$72.90
Purchase #7	$143.40	8.609%	$155.7453	$155.75	$155.75	$155.70
7 purchase totals =	$669.96		$719.5994	$719.61	$719.60	$719.60