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	$26.67	8.366%	$28.9012	$28.90	$28.90	$28.90
Purchase #2	$171.48	11.204%	$190.6926	$190.69	$190.70	$190.70
Purchase #3	$41.33	3.676%	$42.8493	$42.85	$42.85	$42.80
Purchase #4	$143.87	7.222%	$154.2603	$154.26	$154.25	$154.30
Purchase #5	$102.83	4.495%	$107.4522	$107.45	$107.45	$107.50
Purchase #6	$18.35	3.157%	$18.9293	$18.93	$18.95	$18.90
Purchase #7	$158.89	5.147%	$167.0681	$167.07	$167.05	$167.10
7 purchase totals =	$663.42		$710.1530	$710.15	$710.15	$710.20