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	$10.61	9.325%	$11.5994	$11.60	$11.60	$11.60
Purchase #2	$154.90	11.422%	$172.5927	$172.59	$172.60	$172.60
Purchase #3	$235.28	6.179%	$249.818	$249.82	$249.80	$249.80
Purchase #4	$216.45	9.303%	$236.5863	$236.59	$236.60	$236.60
Purchase #5	$130.34	13.311%	$147.6896	$147.69	$147.70	$147.70
Purchase #6	$13.51	7.451%	$14.5166	$14.52	$14.50	$14.50
Purchase #7	$124.36	10.526%	$137.4501	$137.45	$137.45	$137.50
7 purchase totals =	$885.45		$970.2527	$970.26	$970.25	$970.30