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	$72.83	10.494%	$80.4728	$80.47	$80.45	$80.50
Purchase #2	$12.29	5.252%	$12.9355	$12.94	$12.95	$12.90
Purchase #3	$131.51	6.342%	$139.8504	$139.85	$139.85	$139.90
Purchase #4	$186.30	9.375%	$203.7656	$203.77	$203.75	$203.80
Purchase #5	$220.55	4.689%	$230.8916	$230.89	$230.90	$230.90
Purchase #6	$47.57	9.791%	$52.2276	$52.23	$52.25	$52.20
Purchase #7	$87.90	8.253%	$95.1544	$95.15	$95.15	$95.20
7 purchase totals =	$758.95		$815.2979	$815.30	$815.30	$815.40