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	$19.61	12.543%	$22.0697	$22.07	$22.05	$22.10
Purchase #2	$15.93	8.520%	$17.2872	$17.29	$17.30	$17.30
Purchase #3	$6.75	6.191%	$7.1679	$7.17	$7.15	$7.20
Purchase #4	$118.30	8.594%	$128.4667	$128.47	$128.45	$128.50
Purchase #5	$77.48	10.202%	$85.3845	$85.38	$85.40	$85.40
Purchase #6	$7.52	4.406%	$7.8513	$7.85	$7.85	$7.90
Purchase #7	$40.86	3.830%	$42.4249	$42.42	$42.40	$42.40
7 purchase totals =	$286.45		$310.6522	$310.65	$310.60	$310.80