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	$48.58	12.178%	$54.4961	$54.50	$54.50	$54.50
Purchase #2	$11.98	4.211%	$12.4845	$12.48	$12.50	$12.50
Purchase #3	$176.28	10.261%	$194.3681	$194.37	$194.35	$194.40
Purchase #4	$235.25	13.247%	$266.4136	$266.41	$266.40	$266.40
Purchase #5	$227.39	6.557%	$242.3	$242.30	$242.30	$242.30
Purchase #6	$139.53	13.246%	$158.0121	$158.01	$158.00	$158.00
Purchase #7	$11.47	7.272%	$12.3041	$12.30	$12.30	$12.30
7 purchase totals =	$850.48		$940.3785	$940.37	$940.35	$940.40