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	$51.67	6.240%	$54.8942	$54.89	$54.90	$54.90
Purchase #2	$30.39	10.439%	$33.5624	$33.56	$33.55	$33.60
Purchase #3	$22.45	5.594%	$23.7059	$23.71	$23.70	$23.70
Purchase #4	$154.60	9.802%	$169.7539	$169.75	$169.75	$169.80
Purchase #5	$60.81	8.290%	$65.8511	$65.85	$65.85	$65.90
Purchase #6	$54.32	9.411%	$59.4321	$59.43	$59.45	$59.40
Purchase #7	$28.92	13.495%	$32.8228	$32.82	$32.80	$32.80
7 purchase totals =	$403.16		$440.0224	$440.01	$440.00	$440.10