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	$106.49	5.327%	$112.1627	$112.16	$112.15	$112.20
Purchase #2	$64.38	4.523%	$67.2919	$67.29	$67.30	$67.30
Purchase #3	$143.66	9.248%	$156.9457	$156.95	$156.95	$156.90
Purchase #4	$235.49	10.682%	$260.645	$260.65	$260.65	$260.60
Purchase #5	$18.67	3.773%	$19.3744	$19.37	$19.35	$19.40
Purchase #6	$113.69	12.392%	$127.7785	$127.78	$127.80	$127.80
Purchase #7	$239.81	6.528%	$255.4648	$255.46	$255.45	$255.50
7 purchase totals =	$922.19		$999.6630	$999.66	$999.65	$999.70