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	$30.71	5.738%	$32.4721	$32.47	$32.45	$32.50
Purchase #2	$40.54	4.341%	$42.2998	$42.30	$42.30	$42.30
Purchase #3	$145.29	9.270%	$158.7584	$158.76	$158.75	$158.80
Purchase #4	$129.74	3.187%	$133.8748	$133.87	$133.85	$133.90
Purchase #5	$117.52	10.175%	$129.4777	$129.48	$129.50	$129.50
Purchase #6	$181.31	9.814%	$199.1038	$199.10	$199.10	$199.10
Purchase #7	$152.52	4.866%	$159.9416	$159.94	$159.95	$159.90
7 purchase totals =	$797.63		$855.9282	$855.92	$855.90	$856.00