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	$155.51	11.164%	$172.8711	$172.87	$172.85	$172.90
Purchase #2	$29.42	10.737%	$32.5788	$32.58	$32.60	$32.60
Purchase #3	$87.90	10.591%	$97.2095	$97.21	$97.20	$97.20
Purchase #4	$37.78	5.504%	$39.8594	$39.86	$39.85	$39.90
Purchase #5	$65.86	7.162%	$70.5769	$70.58	$70.60	$70.60
Purchase #6	$37.37	12.196%	$41.9276	$41.93	$41.95	$41.90
Purchase #7	$136.48	10.614%	$150.966	$150.97	$150.95	$151.00
7 purchase totals =	$550.32		$605.9893	$606.00	$606.00	$606.10