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	$228.78	11.830%	$255.8447	$255.84	$255.85	$255.80
Purchase #2	$61.28	3.587%	$63.4781	$63.48	$63.50	$63.50
Purchase #3	$213.73	7.149%	$229.0096	$229.01	$229.00	$229.00
Purchase #4	$32.28	6.164%	$34.2697	$34.27	$34.25	$34.30
Purchase #5	$34.81	10.854%	$38.5883	$38.59	$38.60	$38.60
Purchase #6	$174.63	3.470%	$180.6897	$180.69	$180.70	$180.70
Purchase #7	$111.39	6.401%	$118.5201	$118.52	$118.50	$118.50
7 purchase totals =	$856.90		$920.4002	$920.40	$920.40	$920.40