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	$54.83	12.338%	$61.5949	$61.59	$61.60	$61.60
Purchase #2	$38.85	9.706%	$42.6208	$42.62	$42.60	$42.60
Purchase #3	$177.70	12.218%	$199.4114	$199.41	$199.40	$199.40
Purchase #4	$32.97	12.536%	$37.1031	$37.10	$37.10	$37.10
Purchase #5	$37.78	13.416%	$42.8486	$42.85	$42.85	$42.80
Purchase #6	$204.89	6.735%	$218.6893	$218.69	$218.70	$218.70
Purchase #7	$227.34	3.814%	$236.0107	$236.01	$236.00	$236.00
7 purchase totals =	$774.36		$838.2788	$838.27	$838.25	$838.20