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	$66.89	8.153%	$72.3435	$72.34	$72.35	$72.30
Purchase #2	$51.60	9.235%	$56.3653	$56.37	$56.35	$56.40
Purchase #3	$102.42	8.794%	$111.4268	$111.43	$111.45	$111.40
Purchase #4	$37.78	4.175%	$39.3573	$39.36	$39.35	$39.40
Purchase #5	$34.64	10.506%	$38.2793	$38.28	$38.30	$38.30
Purchase #6	$107.58	3.755%	$111.6196	$111.62	$111.60	$111.60
Purchase #7	$111.73	4.197%	$116.4193	$116.42	$116.40	$116.40
7 purchase totals =	$512.64		$545.8111	$545.82	$545.80	$545.80