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	$63.57	12.662%	$71.6192	$71.62	$71.60	$71.60
Purchase #2	$81.92	5.563%	$86.4772	$86.48	$86.50	$86.50
Purchase #3	$128.79	11.397%	$143.4682	$143.47	$143.45	$143.50
Purchase #4	$23.96	12.680%	$26.9981	$27.00	$27.00	$27.00
Purchase #5	$18.83	4.300%	$19.6397	$19.64	$19.65	$19.60
Purchase #6	$13.50	10.277%	$14.8874	$14.89	$14.90	$14.90
Purchase #7	$183.58	7.245%	$196.8804	$196.88	$196.90	$196.90
7 purchase totals =	$514.15		$559.9702	$559.98	$560.00	$560.00