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	$35.91	12.821%	$40.514	$40.51	$40.50	$40.50
Purchase #2	$183.85	13.456%	$208.5889	$208.59	$208.60	$208.60
Purchase #3	$196.60	13.171%	$222.4942	$222.49	$222.50	$222.50
Purchase #4	$29.76	10.164%	$32.7848	$32.78	$32.80	$32.80
Purchase #5	$157.86	3.338%	$163.1294	$163.13	$163.15	$163.10
Purchase #6	$222.75	8.220%	$241.0601	$241.06	$241.05	$241.10
Purchase #7	$70.92	7.754%	$76.4191	$76.42	$76.40	$76.40
7 purchase totals =	$897.65		$984.9905	$984.98	$985.00	$985.00