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	$110.90	8.551%	$120.3831	$120.38	$120.40	$120.40
Purchase #2	$120.83	13.265%	$136.8581	$136.86	$136.85	$136.90
Purchase #3	$208.39	6.527%	$221.9916	$221.99	$222.00	$222.00
Purchase #4	$18.68	4.732%	$19.5639	$19.56	$19.55	$19.60
Purchase #5	$64.45	10.733%	$71.3674	$71.37	$71.35	$71.40
Purchase #6	$100.44	11.491%	$111.9816	$111.98	$112.00	$112.00
Purchase #7	$63.54	13.778%	$72.2945	$72.29	$72.30	$72.30
7 purchase totals =	$687.23		$754.4402	$754.43	$754.45	$754.60