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	$12.76	4.472%	$13.3306	$13.33	$13.35	$13.30
Purchase #2	$234.56	4.367%	$244.8032	$244.80	$244.80	$244.80
Purchase #3	$19.35	4.186%	$20.16	$20.16	$20.15	$20.20
Purchase #4	$50.50	12.198%	$56.66	$56.66	$56.65	$56.70
Purchase #5	$241.57	5.747%	$255.453	$255.45	$255.45	$255.50
Purchase #6	$214.45	13.182%	$242.7188	$242.72	$242.70	$242.70
Purchase #7	$34.29	13.228%	$38.8259	$38.83	$38.85	$38.80
7 purchase totals =	$807.48		$871.9515	$871.95	$871.95	$872.00