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	$36.48	6.582%	$38.8811	$38.88	$38.90	$38.90
Purchase #2	$70.31	9.645%	$77.0914	$77.09	$77.10	$77.10
Purchase #3	$71.57	6.649%	$76.3287	$76.33	$76.35	$76.30
Purchase #4	$50.72	7.159%	$54.351	$54.35	$54.35	$54.40
Purchase #5	$113.29	11.248%	$126.0329	$126.03	$126.05	$126.00
Purchase #6	$244.45	4.509%	$255.4723	$255.47	$255.45	$255.50
Purchase #7	$151.55	6.169%	$160.8991	$160.90	$160.90	$160.90
7 purchase totals =	$738.37		$789.0565	$789.05	$789.10	$789.10