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	$29.96	6.163%	$31.8064	$31.81	$31.80	$31.80
Purchase #2	$124.49	13.653%	$141.4866	$141.49	$141.50	$141.50
Purchase #3	$34.30	13.866%	$39.056	$39.06	$39.05	$39.10
Purchase #4	$173.59	13.232%	$196.5594	$196.56	$196.55	$196.60
Purchase #5	$213.70	13.659%	$242.8893	$242.89	$242.90	$242.90
Purchase #6	$41.83	12.625%	$47.111	$47.11	$47.10	$47.10
Purchase #7	$232.29	10.798%	$257.3727	$257.37	$257.35	$257.40
7 purchase totals =	$850.16		$956.2814	$956.29	$956.25	$956.40