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	$12.52	7.850%	$13.5028	$13.50	$13.50	$13.50
Purchase #2	$185.57	4.548%	$194.0097	$194.01	$194.00	$194.00
Purchase #3	$55.45	11.246%	$61.6859	$61.69	$61.70	$61.70
Purchase #4	$48.74	6.859%	$52.0831	$52.08	$52.10	$52.10
Purchase #5	$34.32	9.337%	$37.5245	$37.52	$37.50	$37.50
Purchase #6	$36.93	13.554%	$41.9355	$41.94	$41.95	$41.90
Purchase #7	$53.38	5.287%	$56.2022	$56.20	$56.20	$56.20
7 purchase totals =	$426.91		$456.9437	$456.94	$456.95	$456.90