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	$169.37	8.549%	$183.8494	$183.85	$183.85	$183.80
Purchase #2	$86.95	8.209%	$94.0877	$94.09	$94.10	$94.10
Purchase #3	$141.66	13.457%	$160.7232	$160.72	$160.70	$160.70
Purchase #4	$106.48	4.581%	$111.3578	$111.36	$111.35	$111.40
Purchase #5	$29.36	6.158%	$31.168	$31.17	$31.15	$31.20
Purchase #6	$197.31	12.806%	$222.5775	$222.58	$222.60	$222.60
Purchase #7	$10.29	10.497%	$11.3701	$11.37	$11.35	$11.40
7 purchase totals =	$741.42		$815.1337	$815.14	$815.10	$815.20