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	$95.80	3.742%	$99.3848	$99.38	$99.40	$99.40
Purchase #2	$165.83	11.237%	$184.4643	$184.46	$184.45	$184.50
Purchase #3	$39.92	11.748%	$44.6098	$44.61	$44.60	$44.60
Purchase #4	$59.28	12.806%	$66.8714	$66.87	$66.85	$66.90
Purchase #5	$76.66	13.583%	$87.0727	$87.07	$87.05	$87.10
Purchase #6	$72.90	10.290%	$80.4014	$80.40	$80.40	$80.40
Purchase #7	$42.61	10.333%	$47.0129	$47.01	$47.00	$47.00
7 purchase totals =	$553.00		$609.8173	$609.80	$609.75	$609.90