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	$13.94	11.689%	$15.5694	$15.57	$15.55	$15.60
Purchase #2	$146.52	3.541%	$151.7083	$151.71	$151.70	$151.70
Purchase #3	$230.65	5.176%	$242.5884	$242.59	$242.60	$242.60
Purchase #4	$48.88	13.535%	$55.4959	$55.50	$55.50	$55.50
Purchase #5	$139.35	13.692%	$158.4298	$158.43	$158.45	$158.40
Purchase #6	$201.91	12.810%	$227.7747	$227.77	$227.75	$227.80
Purchase #7	$56.90	8.755%	$61.8816	$61.88	$61.90	$61.90
7 purchase totals =	$838.15		$913.4481	$913.45	$913.45	$913.50