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	$239.52	4.168%	$249.5032	$249.50	$249.50	$249.50
Purchase #2	$65.55	8.223%	$70.9402	$70.94	$70.95	$70.90
Purchase #3	$13.37	6.671%	$14.2619	$14.26	$14.25	$14.30
Purchase #4	$44.75	8.577%	$48.5882	$48.59	$48.60	$48.60
Purchase #5	$155.27	10.839%	$172.0997	$172.10	$172.10	$172.10
Purchase #6	$18.85	13.143%	$21.3275	$21.33	$21.35	$21.30
Purchase #7	$137.31	10.599%	$151.8635	$151.86	$151.85	$151.90
7 purchase totals =	$674.62		$728.5842	$728.58	$728.60	$728.60