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	$132.98	10.421%	$146.8378	$146.84	$146.85	$146.80
Purchase #2	$244.60	13.808%	$278.3744	$278.37	$278.35	$278.40
Purchase #3	$69.43	4.716%	$72.7043	$72.70	$72.70	$72.70
Purchase #4	$115.81	11.293%	$128.8884	$128.89	$128.90	$128.90
Purchase #5	$41.94	11.747%	$46.8667	$46.87	$46.85	$46.90
Purchase #6	$74.83	11.508%	$83.4414	$83.44	$83.45	$83.40
Purchase #7	$19.31	12.310%	$21.6871	$21.69	$21.70	$21.70
7 purchase totals =	$698.90		$778.8001	$778.80	$778.80	$778.80