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	$246.66	12.262%	$276.9054	$276.91	$276.90	$276.90
Purchase #2	$63.71	7.569%	$68.5322	$68.53	$68.55	$68.50
Purchase #3	$106.98	4.354%	$111.6379	$111.64	$111.65	$111.60
Purchase #4	$90.83	8.574%	$98.6178	$98.62	$98.60	$98.60
Purchase #5	$152.86	7.762%	$164.725	$164.73	$164.75	$164.70
Purchase #6	$51.94	5.840%	$54.9733	$54.97	$54.95	$55.00
Purchase #7	$49.77	13.370%	$56.4242	$56.42	$56.40	$56.40
7 purchase totals =	$762.75		$831.8158	$831.82	$831.80	$831.70