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	$39.60	9.768%	$43.4681	$43.47	$43.45	$43.50
Purchase #2	$148.54	13.841%	$169.0994	$169.10	$169.10	$169.10
Purchase #3	$58.82	13.605%	$66.8225	$66.82	$66.80	$66.80
Purchase #4	$86.58	4.215%	$90.2293	$90.23	$90.25	$90.20
Purchase #5	$95.51	8.613%	$103.7363	$103.74	$103.75	$103.70
Purchase #6	$126.99	9.676%	$139.2776	$139.28	$139.30	$139.30
Purchase #7	$48.68	10.471%	$53.7773	$53.78	$53.80	$53.80
7 purchase totals =	$604.72		$666.4105	$666.42	$666.45	$666.40