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	$20.60	5.654%	$21.7647	$21.76	$21.75	$21.80
Purchase #2	$127.36	12.691%	$143.5233	$143.52	$143.50	$143.50
Purchase #3	$92.94	5.292%	$97.8584	$97.86	$97.85	$97.90
Purchase #4	$54.55	13.406%	$61.863	$61.86	$61.85	$61.90
Purchase #5	$132.85	6.225%	$141.1199	$141.12	$141.10	$141.10
Purchase #6	$138.89	12.334%	$156.0207	$156.02	$156.00	$156.00
Purchase #7	$89.93	6.596%	$95.8618	$95.86	$95.85	$95.90
7 purchase totals =	$657.12		$718.0118	$718.00	$717.90	$718.10