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	$142.51	8.867%	$155.1464	$155.15	$155.15	$155.10
Purchase #2	$173.92	3.209%	$179.5011	$179.50	$179.50	$179.50
Purchase #3	$74.38	10.722%	$82.355	$82.36	$82.35	$82.40
Purchase #4	$247.66	7.471%	$266.1627	$266.16	$266.15	$266.20
Purchase #5	$24.65	4.528%	$25.7662	$25.77	$25.75	$25.80
Purchase #6	$165.32	4.390%	$172.5775	$172.58	$172.60	$172.60
Purchase #7	$74.50	5.196%	$78.371	$78.37	$78.35	$78.40
7 purchase totals =	$902.94		$959.8799	$959.89	$959.85	$960.00