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	$78.65	5.406%	$82.9018	$82.90	$82.90	$82.90
Purchase #2	$244.34	4.785%	$256.0317	$256.03	$256.05	$256.00
Purchase #3	$108.84	13.616%	$123.6597	$123.66	$123.65	$123.70
Purchase #4	$135.57	6.265%	$144.0635	$144.06	$144.05	$144.10
Purchase #5	$117.76	12.170%	$132.0914	$132.09	$132.10	$132.10
Purchase #6	$156.54	11.426%	$174.4263	$174.43	$174.45	$174.40
Purchase #7	$43.52	6.636%	$46.408	$46.41	$46.40	$46.40
7 purchase totals =	$885.22		$959.5824	$959.58	$959.60	$959.60