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	$231.41	10.130%	$254.8518	$254.85	$254.85	$254.90
Purchase #2	$93.53	13.154%	$105.8329	$105.83	$105.85	$105.80
Purchase #3	$87.90	3.300%	$90.8007	$90.80	$90.80	$90.80
Purchase #4	$219.40	12.436%	$246.6846	$246.68	$246.70	$246.70
Purchase #5	$247.58	9.198%	$270.3524	$270.35	$270.35	$270.40
Purchase #6	$217.94	3.456%	$225.472	$225.47	$225.45	$225.50
Purchase #7	$217.52	8.170%	$235.2914	$235.29	$235.30	$235.30
7 purchase totals =	$1,315.28		$1,429.2858	$1,429.27	$1,429.30	$1,429.40