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	$29.29	12.389%	$32.9187	$32.92	$32.90	$32.90
Purchase #2	$137.45	12.391%	$154.4814	$154.48	$154.50	$154.50
Purchase #3	$236.52	7.712%	$254.7604	$254.76	$254.75	$254.80
Purchase #4	$153.42	3.382%	$158.6087	$158.61	$158.60	$158.60
Purchase #5	$143.33	13.650%	$162.8945	$162.89	$162.90	$162.90
Purchase #6	$183.51	8.835%	$199.7231	$199.72	$199.70	$199.70
Purchase #7	$249.80	10.118%	$275.0748	$275.07	$275.05	$275.10
7 purchase totals =	$1,133.32		$1,238.4616	$1,238.45	$1,238.40	$1,238.50