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	$45.61	11.797%	$50.9906	$50.99	$51.00	$51.00
Purchase #2	$132.64	6.678%	$141.4977	$141.50	$141.50	$141.50
Purchase #3	$250.46	13.738%	$284.8682	$284.87	$284.85	$284.90
Purchase #4	$140.36	3.763%	$145.6417	$145.64	$145.65	$145.60
Purchase #5	$29.67	13.450%	$33.6606	$33.66	$33.65	$33.70
Purchase #6	$198.90	12.765%	$224.2896	$224.29	$224.30	$224.30
Purchase #7	$90.27	8.402%	$97.8545	$97.85	$97.85	$97.90
7 purchase totals =	$887.91		$978.8029	$978.80	$978.80	$978.90