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	$199.61	12.486%	$224.5333	$224.53	$224.55	$224.50
Purchase #2	$10.53	13.563%	$11.9582	$11.96	$11.95	$12.00
Purchase #3	$106.45	4.845%	$111.6075	$111.61	$111.60	$111.60
Purchase #4	$69.52	3.642%	$72.0519	$72.05	$72.05	$72.10
Purchase #5	$175.75	7.785%	$189.4321	$189.43	$189.45	$189.40
Purchase #6	$35.70	11.785%	$39.9072	$39.91	$39.90	$39.90
Purchase #7	$233.34	8.262%	$252.6186	$252.62	$252.60	$252.60
7 purchase totals =	$830.90		$902.1088	$902.11	$902.10	$902.10