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	$45.97	8.610%	$49.928	$49.93	$49.95	$49.90
Purchase #2	$130.96	11.846%	$146.4735	$146.47	$146.45	$146.50
Purchase #3	$147.86	13.347%	$167.5949	$167.59	$167.60	$167.60
Purchase #4	$132.59	3.687%	$137.4786	$137.48	$137.50	$137.50
Purchase #5	$184.74	7.768%	$199.0906	$199.09	$199.10	$199.10
Purchase #6	$174.97	12.451%	$196.7555	$196.76	$196.75	$196.80
Purchase #7	$14.65	10.822%	$16.2354	$16.24	$16.25	$16.20
7 purchase totals =	$831.74		$913.5565	$913.56	$913.60	$913.60