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	$41.72	9.835%	$45.8232	$45.82	$45.80	$45.80
Purchase #2	$14.42	3.387%	$14.9084	$14.91	$14.90	$14.90
Purchase #3	$155.76	7.517%	$167.4685	$167.47	$167.45	$167.50
Purchase #4	$97.49	11.385%	$108.5892	$108.59	$108.60	$108.60
Purchase #5	$77.76	4.515%	$81.2709	$81.27	$81.25	$81.30
Purchase #6	$19.89	7.614%	$21.4044	$21.40	$21.40	$21.40
Purchase #7	$217.91	10.540%	$240.8777	$240.88	$240.90	$240.90
7 purchase totals =	$624.95		$680.3423	$680.34	$680.30	$680.40