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	$11.95	12.646%	$13.4612	$13.46	$13.45	$13.50
Purchase #2	$119.30	10.856%	$132.2512	$132.25	$132.25	$132.30
Purchase #3	$109.32	7.549%	$117.5726	$117.57	$117.55	$117.60
Purchase #4	$116.47	5.677%	$123.082	$123.08	$123.10	$123.10
Purchase #5	$22.95	12.623%	$25.847	$25.85	$25.85	$25.80
Purchase #6	$54.52	11.395%	$60.7326	$60.73	$60.75	$60.70
Purchase #7	$18.59	11.189%	$20.67	$20.67	$20.65	$20.70
7 purchase totals =	$453.10		$493.6166	$493.61	$493.60	$493.70