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	$52.80	3.247%	$54.5144	$54.51	$54.50	$54.50
Purchase #2	$87.61	5.366%	$92.3112	$92.31	$92.30	$92.30
Purchase #3	$108.72	8.363%	$117.8123	$117.81	$117.80	$117.80
Purchase #4	$53.62	4.594%	$56.0833	$56.08	$56.10	$56.10
Purchase #5	$186.71	13.396%	$211.7217	$211.72	$211.70	$211.70
Purchase #6	$48.70	4.497%	$50.89	$50.89	$50.90	$50.90
Purchase #7	$217.60	5.567%	$229.7138	$229.71	$229.70	$229.70
7 purchase totals =	$755.76		$813.0467	$813.03	$813.00	$813.00