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	$145.35	10.189%	$160.1597	$160.16	$160.15	$160.20
Purchase #2	$95.29	5.576%	$100.6034	$100.60	$100.60	$100.60
Purchase #3	$144.90	5.278%	$152.5478	$152.55	$152.55	$152.50
Purchase #4	$11.53	4.739%	$12.0764	$12.08	$12.10	$12.10
Purchase #5	$161.93	7.349%	$173.8302	$173.83	$173.85	$173.80
Purchase #6	$83.89	10.414%	$92.6263	$92.63	$92.65	$92.60
Purchase #7	$235.73	6.741%	$251.6206	$251.62	$251.60	$251.60
7 purchase totals =	$878.62		$943.4644	$943.47	$943.50	$943.40