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	$48.41	7.797%	$52.1845	$52.18	$52.20	$52.20
Purchase #2	$54.27	9.228%	$59.278	$59.28	$59.30	$59.30
Purchase #3	$139.73	4.827%	$146.4748	$146.47	$146.45	$146.50
Purchase #4	$146.85	8.820%	$159.8022	$159.80	$159.80	$159.80
Purchase #5	$176.25	8.283%	$190.8488	$190.85	$190.85	$190.80
Purchase #6	$135.67	11.671%	$151.504	$151.50	$151.50	$151.50
Purchase #7	$162.62	6.246%	$172.7772	$172.78	$172.80	$172.80
7 purchase totals =	$863.80		$932.8695	$932.86	$932.90	$932.90