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	$93.64	6.187%	$99.4335	$99.43	$99.45	$99.40
Purchase #2	$43.84	11.446%	$48.8579	$48.86	$48.85	$48.90
Purchase #3	$106.66	4.703%	$111.6762	$111.68	$111.70	$111.70
Purchase #4	$42.52	9.730%	$46.6572	$46.66	$46.65	$46.70
Purchase #5	$128.81	9.845%	$141.4913	$141.49	$141.50	$141.50
Purchase #6	$144.56	13.409%	$163.9441	$163.94	$163.95	$163.90
Purchase #7	$82.91	6.401%	$88.2171	$88.22	$88.20	$88.20
7 purchase totals =	$642.94		$700.2773	$700.28	$700.30	$700.30