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	$242.39	12.372%	$272.3785	$272.38	$272.40	$272.40
Purchase #2	$73.87	10.354%	$81.5185	$81.52	$81.50	$81.50
Purchase #3	$176.65	12.721%	$199.1216	$199.12	$199.10	$199.10
Purchase #4	$56.62	5.772%	$59.8881	$59.89	$59.90	$59.90
Purchase #5	$86.79	4.364%	$90.5775	$90.58	$90.60	$90.60
Purchase #6	$16.38	3.421%	$16.9404	$16.94	$16.95	$16.90
Purchase #7	$45.75	13.494%	$51.9235	$51.92	$51.90	$51.90
7 purchase totals =	$698.45		$772.3481	$772.35	$772.35	$772.30