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	$225.46	13.497%	$255.8903	$255.89	$255.90	$255.90
Purchase #2	$57.88	10.330%	$63.859	$63.86	$63.85	$63.90
Purchase #3	$143.97	4.609%	$150.6056	$150.61	$150.60	$150.60
Purchase #4	$125.47	4.703%	$131.3709	$131.37	$131.35	$131.40
Purchase #5	$104.48	8.416%	$113.273	$113.27	$113.25	$113.30
Purchase #6	$109.92	6.368%	$116.9197	$116.92	$116.90	$116.90
Purchase #7	$85.96	11.615%	$95.9443	$95.94	$95.95	$95.90
7 purchase totals =	$853.14		$927.8628	$927.86	$927.80	$927.90