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	$48.86	6.199%	$51.8888	$51.89	$51.90	$51.90
Purchase #2	$40.68	4.726%	$42.6025	$42.60	$42.60	$42.60
Purchase #3	$19.91	8.594%	$21.6211	$21.62	$21.60	$21.60
Purchase #4	$156.67	9.212%	$171.1024	$171.10	$171.10	$171.10
Purchase #5	$132.71	5.502%	$140.0117	$140.01	$140.00	$140.00
Purchase #6	$74.34	10.338%	$82.0253	$82.03	$82.05	$82.00
Purchase #7	$155.53	3.153%	$160.4339	$160.43	$160.45	$160.40
7 purchase totals =	$628.70		$669.6857	$669.68	$669.70	$669.60