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	$232.62	9.128%	$253.8536	$253.85	$253.85	$253.90
Purchase #2	$25.52	8.800%	$27.7658	$27.77	$27.75	$27.80
Purchase #3	$79.34	12.697%	$89.4138	$89.41	$89.40	$89.40
Purchase #4	$37.60	9.703%	$41.2483	$41.25	$41.25	$41.20
Purchase #5	$10.72	4.545%	$11.2072	$11.21	$11.20	$11.20
Purchase #6	$132.87	6.832%	$141.9477	$141.95	$141.95	$141.90
Purchase #7	$93.95	10.147%	$103.4831	$103.48	$103.50	$103.50
7 purchase totals =	$612.62		$668.9195	$668.92	$668.90	$668.90