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	$229.54	12.868%	$259.0772	$259.08	$259.10	$259.10
Purchase #2	$179.78	11.748%	$200.9006	$200.90	$200.90	$200.90
Purchase #3	$13.89	12.233%	$15.5892	$15.59	$15.60	$15.60
Purchase #4	$108.83	3.261%	$112.3789	$112.38	$112.40	$112.40
Purchase #5	$200.42	13.311%	$227.0979	$227.10	$227.10	$227.10
Purchase #6	$10.62	13.610%	$12.0654	$12.07	$12.05	$12.10
Purchase #7	$119.47	4.863%	$125.2798	$125.28	$125.30	$125.30
7 purchase totals =	$862.55		$952.3890	$952.40	$952.45	$952.50