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	$103.84	9.188%	$113.3808	$113.38	$113.40	$113.40
Purchase #2	$203.81	13.638%	$231.6056	$231.61	$231.60	$231.60
Purchase #3	$83.31	7.380%	$89.4583	$89.46	$89.45	$89.50
Purchase #4	$194.83	6.175%	$206.8608	$206.86	$206.85	$206.90
Purchase #5	$146.86	8.160%	$158.8438	$158.84	$158.85	$158.80
Purchase #6	$47.63	8.456%	$51.6576	$51.66	$51.65	$51.70
Purchase #7	$83.48	6.238%	$88.6875	$88.69	$88.70	$88.70
7 purchase totals =	$863.76		$940.4944	$940.50	$940.50	$940.60