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	$59.60	7.249%	$63.9204	$63.92	$63.90	$63.90
Purchase #2	$52.53	6.624%	$56.0096	$56.01	$56.00	$56.00
Purchase #3	$105.63	5.151%	$111.071	$111.07	$111.05	$111.10
Purchase #4	$43.50	11.794%	$48.6304	$48.63	$48.65	$48.60
Purchase #5	$53.46	11.525%	$59.6213	$59.62	$59.60	$59.60
Purchase #6	$149.66	12.794%	$168.8075	$168.81	$168.80	$168.80
Purchase #7	$118.59	8.773%	$128.9939	$128.99	$129.00	$129.00
7 purchase totals =	$582.97		$637.0541	$637.05	$637.00	$637.00