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	$105.88	5.680%	$111.894	$111.89	$111.90	$111.90
Purchase #2	$7.41	3.849%	$7.6952	$7.70	$7.70	$7.70
Purchase #3	$87.51	13.722%	$99.5181	$99.52	$99.50	$99.50
Purchase #4	$231.78	3.510%	$239.9155	$239.92	$239.90	$239.90
Purchase #5	$130.42	6.247%	$138.5673	$138.57	$138.55	$138.60
Purchase #6	$10.95	8.441%	$11.8743	$11.87	$11.85	$11.90
Purchase #7	$30.77	13.106%	$34.8027	$34.80	$34.80	$34.80
7 purchase totals =	$604.72		$644.2671	$644.27	$644.20	$644.30