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	$135.36	9.467%	$148.1745	$148.17	$148.15	$148.20
Purchase #2	$158.52	13.432%	$179.8124	$179.81	$179.80	$179.80
Purchase #3	$151.78	9.434%	$166.0989	$166.10	$166.10	$166.10
Purchase #4	$44.87	7.395%	$48.1881	$48.19	$48.20	$48.20
Purchase #5	$125.27	4.111%	$130.4198	$130.42	$130.40	$130.40
Purchase #6	$228.72	13.179%	$258.863	$258.86	$258.85	$258.90
Purchase #7	$44.67	4.664%	$46.7534	$46.75	$46.75	$46.80
7 purchase totals =	$889.19		$978.3101	$978.30	$978.25	$978.40