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	$19.71	8.846%	$21.4535	$21.45	$21.45	$21.50
Purchase #2	$33.49	10.538%	$37.0192	$37.02	$37.00	$37.00
Purchase #3	$64.38	6.553%	$68.5988	$68.60	$68.60	$68.60
Purchase #4	$102.65	11.290%	$114.2392	$114.24	$114.25	$114.20
Purchase #5	$152.59	13.627%	$173.3834	$173.38	$173.40	$173.40
Purchase #6	$241.27	7.131%	$258.475	$258.48	$258.50	$258.50
Purchase #7	$6.79	10.243%	$7.4855	$7.49	$7.50	$7.50
7 purchase totals =	$620.88		$680.6546	$680.66	$680.70	$680.70