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	$126.68	3.547%	$131.1733	$131.17	$131.15	$131.20
Purchase #2	$136.46	13.121%	$154.3649	$154.36	$154.35	$154.40
Purchase #3	$138.95	13.600%	$157.8472	$157.85	$157.85	$157.80
Purchase #4	$38.59	5.264%	$40.6214	$40.62	$40.60	$40.60
Purchase #5	$85.29	5.337%	$89.8419	$89.84	$89.85	$89.80
Purchase #6	$210.56	8.519%	$228.4976	$228.50	$228.50	$228.50
Purchase #7	$141.69	11.214%	$157.5791	$157.58	$157.60	$157.60
7 purchase totals =	$878.22		$959.9254	$959.92	$959.90	$959.90