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	$9.52	10.570%	$10.5263	$10.53	$10.55	$10.50
Purchase #2	$154.96	8.514%	$168.1533	$168.15	$168.15	$168.20
Purchase #3	$220.88	3.264%	$228.0895	$228.09	$228.10	$228.10
Purchase #4	$24.60	4.526%	$25.7134	$25.71	$25.70	$25.70
Purchase #5	$154.46	8.425%	$167.4733	$167.47	$167.45	$167.50
Purchase #6	$113.76	8.265%	$123.1623	$123.16	$123.15	$123.20
Purchase #7	$108.78	10.636%	$120.3498	$120.35	$120.35	$120.30
7 purchase totals =	$786.96		$843.4679	$843.46	$843.45	$843.50