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	$33.67	13.273%	$38.139	$38.14	$38.15	$38.10
Purchase #2	$148.59	12.567%	$167.2633	$167.26	$167.25	$167.30
Purchase #3	$128.61	12.393%	$144.5486	$144.55	$144.55	$144.50
Purchase #4	$126.83	11.368%	$141.248	$141.25	$141.25	$141.20
Purchase #5	$50.35	7.594%	$54.1736	$54.17	$54.15	$54.20
Purchase #6	$157.56	6.800%	$168.2741	$168.27	$168.25	$168.30
Purchase #7	$54.56	8.174%	$59.0197	$59.02	$59.00	$59.00
7 purchase totals =	$700.17		$772.6663	$772.66	$772.60	$772.60