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	$85.63	6.854%	$91.4991	$91.50	$91.50	$91.50
Purchase #2	$215.89	10.418%	$238.3814	$238.38	$238.40	$238.40
Purchase #3	$27.38	8.286%	$29.6487	$29.65	$29.65	$29.60
Purchase #4	$161.82	3.856%	$168.0598	$168.06	$168.05	$168.10
Purchase #5	$30.66	5.868%	$32.4591	$32.46	$32.45	$32.50
Purchase #6	$119.89	10.774%	$132.8069	$132.81	$132.80	$132.80
Purchase #7	$208.81	4.128%	$217.4297	$217.43	$217.45	$217.40
7 purchase totals =	$850.08		$910.2847	$910.29	$910.30	$910.30