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	$129.72	10.801%	$143.7311	$143.73	$143.75	$143.70
Purchase #2	$60.50	11.490%	$67.4515	$67.45	$67.45	$67.50
Purchase #3	$128.72	13.183%	$145.6892	$145.69	$145.70	$145.70
Purchase #4	$83.66	9.399%	$91.5232	$91.52	$91.50	$91.50
Purchase #5	$139.43	3.358%	$144.1121	$144.11	$144.10	$144.10
Purchase #6	$212.27	9.500%	$232.4357	$232.44	$232.45	$232.40
Purchase #7	$53.28	8.547%	$57.8338	$57.83	$57.85	$57.80
7 purchase totals =	$807.58		$882.7766	$882.77	$882.80	$882.70