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	$82.81	4.239%	$86.3203	$86.32	$86.30	$86.30
Purchase #2	$154.42	6.377%	$164.2674	$164.27	$164.25	$164.30
Purchase #3	$122.85	11.591%	$137.0895	$137.09	$137.10	$137.10
Purchase #4	$213.60	12.546%	$240.3983	$240.40	$240.40	$240.40
Purchase #5	$136.84	12.561%	$154.0285	$154.03	$154.05	$154.00
Purchase #6	$10.43	4.757%	$10.9262	$10.93	$10.95	$10.90
Purchase #7	$162.52	5.763%	$171.886	$171.89	$171.90	$171.90
7 purchase totals =	$883.47		$964.9162	$964.93	$964.95	$964.90