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	$32.82	5.402%	$34.5929	$34.59	$34.60	$34.60
Purchase #2	$189.28	12.818%	$213.5419	$213.54	$213.55	$213.50
Purchase #3	$38.66	6.636%	$41.2255	$41.23	$41.25	$41.20
Purchase #4	$107.78	4.201%	$112.3078	$112.31	$112.30	$112.30
Purchase #5	$8.99	11.763%	$10.0475	$10.05	$10.05	$10.00
Purchase #6	$116.38	13.278%	$131.8329	$131.83	$131.85	$131.80
Purchase #7	$89.70	9.152%	$97.9093	$97.91	$97.90	$97.90
7 purchase totals =	$583.61		$641.4578	$641.46	$641.50	$641.30