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	$203.79	8.533%	$221.1794	$221.18	$221.20	$221.20
Purchase #2	$243.84	5.387%	$256.9757	$256.98	$257.00	$257.00
Purchase #3	$34.67	11.240%	$38.5669	$38.57	$38.55	$38.60
Purchase #4	$186.95	4.579%	$195.5104	$195.51	$195.50	$195.50
Purchase #5	$20.59	5.292%	$21.6796	$21.68	$21.70	$21.70
Purchase #6	$99.49	6.457%	$105.9141	$105.91	$105.90	$105.90
Purchase #7	$100.44	11.345%	$111.8349	$111.83	$111.85	$111.80
7 purchase totals =	$889.77		$951.6610	$951.66	$951.70	$951.70