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	$138.59	13.756%	$157.6544	$157.65	$157.65	$157.70
Purchase #2	$29.64	6.125%	$31.4555	$31.46	$31.45	$31.50
Purchase #3	$146.92	5.414%	$154.8742	$154.87	$154.85	$154.90
Purchase #4	$146.47	4.759%	$153.4405	$153.44	$153.45	$153.40
Purchase #5	$39.37	4.358%	$41.0857	$41.09	$41.10	$41.10
Purchase #6	$63.50	13.525%	$72.0884	$72.09	$72.10	$72.10
Purchase #7	$119.55	10.272%	$131.8302	$131.83	$131.85	$131.80
7 purchase totals =	$684.04		$742.4289	$742.43	$742.45	$742.50