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	$53.90	5.121%	$56.6602	$56.66	$56.65	$56.70
Purchase #2	$134.36	5.786%	$142.1341	$142.13	$142.15	$142.10
Purchase #3	$19.67	6.297%	$20.9086	$20.91	$20.90	$20.90
Purchase #4	$111.41	13.516%	$126.4682	$126.47	$126.45	$126.50
Purchase #5	$132.25	10.231%	$145.7805	$145.78	$145.80	$145.80
Purchase #6	$227.33	13.357%	$257.6945	$257.69	$257.70	$257.70
Purchase #7	$78.85	12.660%	$88.8324	$88.83	$88.85	$88.80
7 purchase totals =	$757.77		$838.4785	$838.47	$838.50	$838.50