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	$28.38	13.824%	$32.3033	$32.30	$32.30	$32.30
Purchase #2	$78.42	9.587%	$85.9381	$85.94	$85.95	$85.90
Purchase #3	$199.74	4.281%	$208.2909	$208.29	$208.30	$208.30
Purchase #4	$139.56	8.548%	$151.4896	$151.49	$151.50	$151.50
Purchase #5	$249.70	10.445%	$275.7812	$275.78	$275.80	$275.80
Purchase #6	$30.98	3.248%	$31.9862	$31.99	$32.00	$32.00
Purchase #7	$9.91	5.387%	$10.4439	$10.44	$10.45	$10.40
7 purchase totals =	$736.69		$796.2332	$796.23	$796.30	$796.20