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	$12.25	8.329%	$13.2703	$13.27	$13.25	$13.30
Purchase #2	$33.54	11.847%	$37.5135	$37.51	$37.50	$37.50
Purchase #3	$61.67	8.196%	$66.7245	$66.72	$66.70	$66.70
Purchase #4	$35.79	4.294%	$37.3268	$37.33	$37.35	$37.30
Purchase #5	$169.33	12.455%	$190.4201	$190.42	$190.40	$190.40
Purchase #6	$39.78	12.290%	$44.669	$44.67	$44.65	$44.70
Purchase #7	$222.85	11.831%	$249.2154	$249.22	$249.20	$249.20
7 purchase totals =	$575.21		$639.1396	$639.14	$639.05	$639.10