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	$14.61	13.534%	$16.5873	$16.59	$16.60	$16.60
Purchase #2	$95.85	4.762%	$100.4144	$100.41	$100.40	$100.40
Purchase #3	$152.82	10.545%	$168.9349	$168.93	$168.95	$168.90
Purchase #4	$155.81	7.158%	$166.9629	$166.96	$166.95	$167.00
Purchase #5	$231.69	10.849%	$256.826	$256.83	$256.85	$256.80
Purchase #6	$123.89	8.255%	$134.1171	$134.12	$134.10	$134.10
Purchase #7	$128.25	9.699%	$140.689	$140.69	$140.70	$140.70
7 purchase totals =	$902.92		$984.5316	$984.53	$984.55	$984.50