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	$9.37	11.636%	$10.4603	$10.46	$10.45	$10.50
Purchase #2	$138.49	12.492%	$155.7902	$155.79	$155.80	$155.80
Purchase #3	$246.50	6.545%	$262.6334	$262.63	$262.65	$262.60
Purchase #4	$184.66	13.736%	$210.0249	$210.02	$210.00	$210.00
Purchase #5	$214.77	3.176%	$221.5911	$221.59	$221.60	$221.60
Purchase #6	$18.98	13.137%	$21.4734	$21.47	$21.45	$21.50
Purchase #7	$228.59	9.301%	$249.8512	$249.85	$249.85	$249.90
7 purchase totals =	$1,041.36		$1,131.8245	$1,131.81	$1,131.80	$1,131.90