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	$126.64	8.199%	$137.0232	$137.02	$137.00	$137.00
Purchase #2	$89.46	6.723%	$95.4744	$95.47	$95.45	$95.50
Purchase #3	$60.46	4.710%	$63.3077	$63.31	$63.30	$63.30
Purchase #4	$80.99	7.379%	$86.9663	$86.97	$86.95	$87.00
Purchase #5	$16.83	9.716%	$18.4652	$18.47	$18.45	$18.50
Purchase #6	$97.49	7.840%	$105.1332	$105.13	$105.15	$105.10
Purchase #7	$48.56	10.167%	$53.4971	$53.50	$53.50	$53.50
7 purchase totals =	$520.43		$559.8671	$559.87	$559.80	$559.90