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	$98.53	6.791%	$105.2212	$105.22	$105.20	$105.20
Purchase #2	$230.59	3.363%	$238.3447	$238.34	$238.35	$238.30
Purchase #3	$51.39	9.244%	$56.1405	$56.14	$56.15	$56.10
Purchase #4	$21.79	11.269%	$24.2455	$24.25	$24.25	$24.20
Purchase #5	$231.78	10.617%	$256.3881	$256.39	$256.40	$256.40
Purchase #6	$100.52	4.246%	$104.7881	$104.79	$104.80	$104.80
Purchase #7	$159.26	4.331%	$166.1576	$166.16	$166.15	$166.20
7 purchase totals =	$893.86		$951.2857	$951.29	$951.30	$951.20