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	$125.65	11.334%	$139.8912	$139.89	$139.90	$139.90
Purchase #2	$248.53	13.570%	$282.2555	$282.26	$282.25	$282.30
Purchase #3	$66.78	11.638%	$74.5519	$74.55	$74.55	$74.60
Purchase #4	$116.77	13.838%	$132.9286	$132.93	$132.95	$132.90
Purchase #5	$48.52	8.190%	$52.4938	$52.49	$52.50	$52.50
Purchase #6	$17.32	10.215%	$19.0892	$19.09	$19.10	$19.10
Purchase #7	$71.78	9.367%	$78.5036	$78.50	$78.50	$78.50
7 purchase totals =	$695.35		$779.7138	$779.71	$779.75	$779.80