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	$10.61	10.293%	$11.7021	$11.70	$11.70	$11.70
Purchase #2	$62.66	5.158%	$65.892	$65.89	$65.90	$65.90
Purchase #3	$23.32	5.326%	$24.562	$24.56	$24.55	$24.60
Purchase #4	$230.26	4.492%	$240.6033	$240.60	$240.60	$240.60
Purchase #5	$40.37	10.190%	$44.4837	$44.48	$44.50	$44.50
Purchase #6	$149.61	10.171%	$164.8268	$164.83	$164.85	$164.80
Purchase #7	$5.78	11.207%	$6.4278	$6.43	$6.45	$6.40
7 purchase totals =	$522.61		$558.4977	$558.49	$558.55	$558.50