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	$29.82	5.550%	$31.475	$31.48	$31.50	$31.50
Purchase #2	$136.95	4.698%	$143.3839	$143.38	$143.40	$143.40
Purchase #3	$30.30	13.778%	$34.4747	$34.47	$34.45	$34.50
Purchase #4	$161.33	10.130%	$177.6727	$177.67	$177.65	$177.70
Purchase #5	$49.55	4.826%	$51.9413	$51.94	$51.95	$51.90
Purchase #6	$10.87	5.463%	$11.4638	$11.46	$11.45	$11.50
Purchase #7	$66.85	8.489%	$72.5249	$72.52	$72.50	$72.50
7 purchase totals =	$485.67		$522.9363	$522.92	$522.90	$523.00