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	$35.87	13.710%	$40.7878	$40.79	$40.80	$40.80
Purchase #2	$38.87	9.856%	$42.701	$42.70	$42.70	$42.70
Purchase #3	$18.35	5.193%	$19.3029	$19.30	$19.30	$19.30
Purchase #4	$152.99	13.492%	$173.6314	$173.63	$173.65	$173.60
Purchase #5	$40.68	4.452%	$42.4911	$42.49	$42.50	$42.50
Purchase #6	$69.65	4.691%	$72.9173	$72.92	$72.90	$72.90
Purchase #7	$190.82	12.285%	$214.2622	$214.26	$214.25	$214.30
7 purchase totals =	$547.23		$606.0937	$606.09	$606.10	$606.10