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	$123.74	6.238%	$131.4589	$131.46	$131.45	$131.50
Purchase #2	$224.67	11.634%	$250.8081	$250.81	$250.80	$250.80
Purchase #3	$122.40	8.229%	$132.4723	$132.47	$132.45	$132.50
Purchase #4	$55.38	10.220%	$61.0398	$61.04	$61.05	$61.00
Purchase #5	$45.82	13.495%	$52.0034	$52.00	$52.00	$52.00
Purchase #6	$60.52	5.212%	$63.6743	$63.67	$63.65	$63.70
Purchase #7	$158.40	6.578%	$168.8196	$168.82	$168.80	$168.80
7 purchase totals =	$790.93		$860.2764	$860.27	$860.20	$860.30