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	$29.59	8.409%	$32.0782	$32.08	$32.10	$32.10
Purchase #2	$100.51	10.570%	$111.1339	$111.13	$111.15	$111.10
Purchase #3	$92.93	11.458%	$103.5779	$103.58	$103.60	$103.60
Purchase #4	$203.77	11.762%	$227.7374	$227.74	$227.75	$227.70
Purchase #5	$111.25	5.743%	$117.6391	$117.64	$117.65	$117.60
Purchase #6	$51.55	9.123%	$56.2529	$56.25	$56.25	$56.30
Purchase #7	$12.90	9.610%	$14.1397	$14.14	$14.15	$14.10
7 purchase totals =	$602.50		$662.5591	$662.56	$662.65	$662.50