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	$21.86	6.332%	$23.2442	$23.24	$23.25	$23.20
Purchase #2	$199.39	8.174%	$215.6881	$215.69	$215.70	$215.70
Purchase #3	$230.38	12.809%	$259.8894	$259.89	$259.90	$259.90
Purchase #4	$7.25	3.669%	$7.516	$7.52	$7.50	$7.50
Purchase #5	$112.94	4.816%	$118.3792	$118.38	$118.40	$118.40
Purchase #6	$134.71	5.296%	$141.8442	$141.84	$141.85	$141.80
Purchase #7	$139.89	9.713%	$153.4775	$153.48	$153.50	$153.50
7 purchase totals =	$846.42		$920.0386	$920.04	$920.10	$920.00