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	$19.71	4.778%	$20.6517	$20.65	$20.65	$20.70
Purchase #2	$227.67	12.821%	$256.8596	$256.86	$256.85	$256.90
Purchase #3	$206.83	4.863%	$216.8881	$216.89	$216.90	$216.90
Purchase #4	$22.60	10.147%	$24.8932	$24.89	$24.90	$24.90
Purchase #5	$241.56	3.531%	$250.0895	$250.09	$250.10	$250.10
Purchase #6	$87.46	3.108%	$90.1783	$90.18	$90.20	$90.20
Purchase #7	$120.67	10.239%	$133.0254	$133.03	$133.05	$133.00
7 purchase totals =	$926.50		$992.5858	$992.59	$992.65	$992.70