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	$37.59	13.809%	$42.7808	$42.78	$42.80	$42.80
Purchase #2	$57.34	11.547%	$63.961	$63.96	$63.95	$64.00
Purchase #3	$234.94	6.275%	$249.6825	$249.68	$249.70	$249.70
Purchase #4	$247.59	4.571%	$258.9073	$258.91	$258.90	$258.90
Purchase #5	$6.45	8.723%	$7.0126	$7.01	$7.00	$7.00
Purchase #6	$76.71	9.311%	$83.8525	$83.85	$83.85	$83.90
Purchase #7	$20.85	3.704%	$21.6223	$21.62	$21.60	$21.60
7 purchase totals =	$681.47		$727.8190	$727.81	$727.80	$727.90