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	$66.52	6.864%	$71.0859	$71.09	$71.10	$71.10
Purchase #2	$160.83	12.412%	$180.7922	$180.79	$180.80	$180.80
Purchase #3	$136.67	6.278%	$145.2501	$145.25	$145.25	$145.30
Purchase #4	$128.81	9.537%	$141.0946	$141.09	$141.10	$141.10
Purchase #5	$161.32	11.258%	$179.4814	$179.48	$179.50	$179.50
Purchase #6	$6.86	9.121%	$7.4857	$7.49	$7.50	$7.50
Purchase #7	$58.68	3.268%	$60.5977	$60.60	$60.60	$60.60
7 purchase totals =	$719.69		$785.7876	$785.79	$785.85	$785.90