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	$50.49	4.274%	$52.6479	$52.65	$52.65	$52.60
Purchase #2	$161.62	10.650%	$178.8325	$178.83	$178.85	$178.80
Purchase #3	$16.40	11.335%	$18.2589	$18.26	$18.25	$18.30
Purchase #4	$106.91	4.389%	$111.6023	$111.60	$111.60	$111.60
Purchase #5	$38.67	10.367%	$42.6789	$42.68	$42.70	$42.70
Purchase #6	$48.97	3.142%	$50.5086	$50.51	$50.50	$50.50
Purchase #7	$137.39	8.130%	$148.5598	$148.56	$148.55	$148.60
7 purchase totals =	$560.45		$603.0889	$603.09	$603.10	$603.10