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	$111.26	10.680%	$123.1426	$123.14	$123.15	$123.10
Purchase #2	$33.81	6.647%	$36.0574	$36.06	$36.05	$36.10
Purchase #3	$56.67	5.340%	$59.6962	$59.70	$59.70	$59.70
Purchase #4	$47.77	10.717%	$52.8895	$52.89	$52.90	$52.90
Purchase #5	$19.49	13.500%	$22.1212	$22.12	$22.10	$22.10
Purchase #6	$63.37	8.146%	$68.5321	$68.53	$68.55	$68.50
Purchase #7	$127.90	7.717%	$137.77	$137.77	$137.75	$137.80
7 purchase totals =	$460.27		$500.2090	$500.21	$500.20	$500.20