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	$42.63	13.218%	$48.2648	$48.26	$48.25	$48.30
Purchase #2	$56.56	12.509%	$63.6351	$63.64	$63.65	$63.60
Purchase #3	$239.64	3.535%	$248.1113	$248.11	$248.10	$248.10
Purchase #4	$34.92	9.297%	$38.1665	$38.17	$38.15	$38.20
Purchase #5	$90.90	10.518%	$100.4609	$100.46	$100.45	$100.50
Purchase #6	$108.49	7.468%	$116.592	$116.59	$116.60	$116.60
Purchase #7	$33.46	4.475%	$34.9573	$34.96	$34.95	$35.00
7 purchase totals =	$606.60		$650.1879	$650.19	$650.15	$650.30