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	$9.98	4.116%	$10.3908	$10.39	$10.40	$10.40
Purchase #2	$238.82	7.532%	$256.8079	$256.81	$256.80	$256.80
Purchase #3	$85.91	4.643%	$89.8988	$89.90	$89.90	$89.90
Purchase #4	$51.40	9.644%	$56.357	$56.36	$56.35	$56.40
Purchase #5	$105.25	3.504%	$108.938	$108.94	$108.95	$108.90
Purchase #6	$109.90	4.600%	$114.9554	$114.96	$114.95	$115.00
Purchase #7	$15.94	12.221%	$17.888	$17.89	$17.90	$17.90
7 purchase totals =	$617.20		$655.2359	$655.25	$655.25	$655.30