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	$35.25	11.785%	$39.4042	$39.40	$39.40	$39.40
Purchase #2	$31.98	9.728%	$35.091	$35.09	$35.10	$35.10
Purchase #3	$54.95	9.128%	$59.9658	$59.97	$59.95	$60.00
Purchase #4	$76.69	7.405%	$82.3689	$82.37	$82.35	$82.40
Purchase #5	$147.72	9.268%	$161.4107	$161.41	$161.40	$161.40
Purchase #6	$121.73	5.449%	$128.3631	$128.36	$128.35	$128.40
Purchase #7	$76.34	9.363%	$83.4877	$83.49	$83.50	$83.50
7 purchase totals =	$544.66		$590.0914	$590.09	$590.05	$590.20