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	$9.47	11.789%	$10.5864	$10.59	$10.60	$10.60
Purchase #2	$199.71	5.256%	$210.2068	$210.21	$210.20	$210.20
Purchase #3	$47.46	13.593%	$53.9112	$53.91	$53.90	$53.90
Purchase #4	$114.76	12.347%	$128.9294	$128.93	$128.95	$128.90
Purchase #5	$47.52	8.297%	$51.4627	$51.46	$51.45	$51.50
Purchase #6	$183.71	7.147%	$196.8398	$196.84	$196.85	$196.80
Purchase #7	$21.95	11.429%	$24.4587	$24.46	$24.45	$24.50
7 purchase totals =	$624.58		$676.3950	$676.40	$676.40	$676.40