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	$78.92	13.221%	$89.354	$89.35	$89.35	$89.40
Purchase #2	$37.33	12.386%	$41.9537	$41.95	$41.95	$42.00
Purchase #3	$246.74	6.392%	$262.5116	$262.51	$262.50	$262.50
Purchase #4	$204.71	8.363%	$221.8299	$221.83	$221.85	$221.80
Purchase #5	$28.68	13.261%	$32.4833	$32.48	$32.50	$32.50
Purchase #6	$95.81	5.500%	$101.0796	$101.08	$101.10	$101.10
Purchase #7	$22.72	3.244%	$23.457	$23.46	$23.45	$23.50
7 purchase totals =	$714.91		$772.6691	$772.66	$772.70	$772.80