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	$241.62	6.156%	$256.4941	$256.49	$256.50	$256.50
Purchase #2	$133.44	13.809%	$151.8667	$151.87	$151.85	$151.90
Purchase #3	$29.54	10.586%	$32.6671	$32.67	$32.65	$32.70
Purchase #4	$85.90	6.372%	$91.3735	$91.37	$91.35	$91.40
Purchase #5	$95.38	7.564%	$102.5945	$102.59	$102.60	$102.60
Purchase #6	$7.34	4.206%	$7.6487	$7.65	$7.65	$7.60
Purchase #7	$20.51	11.387%	$22.8455	$22.85	$22.85	$22.80
7 purchase totals =	$613.73		$665.4901	$665.49	$665.45	$665.50