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	$242.27	5.603%	$255.8444	$255.84	$255.85	$255.80
Purchase #2	$54.85	9.621%	$60.1271	$60.13	$60.15	$60.10
Purchase #3	$42.25	3.551%	$43.7503	$43.75	$43.75	$43.80
Purchase #4	$149.70	9.293%	$163.6116	$163.61	$163.60	$163.60
Purchase #5	$45.78	11.504%	$51.0465	$51.05	$51.05	$51.00
Purchase #6	$227.71	12.204%	$255.4997	$255.50	$255.50	$255.50
Purchase #7	$63.33	6.866%	$67.6782	$67.68	$67.70	$67.70
7 purchase totals =	$825.89		$897.5578	$897.56	$897.60	$897.50