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	$13.77	10.851%	$15.2642	$15.26	$15.25	$15.30
Purchase #2	$200.96	11.416%	$223.9016	$223.90	$223.90	$223.90
Purchase #3	$38.47	3.548%	$39.8349	$39.83	$39.85	$39.80
Purchase #4	$92.35	8.346%	$100.0575	$100.06	$100.05	$100.10
Purchase #5	$100.81	13.509%	$114.4284	$114.43	$114.45	$114.40
Purchase #6	$96.45	4.314%	$100.6109	$100.61	$100.60	$100.60
Purchase #7	$239.56	8.431%	$259.7573	$259.76	$259.75	$259.80
7 purchase totals =	$782.37		$853.8548	$853.85	$853.85	$853.90