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	$205.77	8.505%	$223.2707	$223.27	$223.25	$223.30
Purchase #2	$21.81	12.804%	$24.6026	$24.60	$24.60	$24.60
Purchase #3	$123.97	6.454%	$131.971	$131.97	$131.95	$132.00
Purchase #4	$53.88	4.865%	$56.5013	$56.50	$56.50	$56.50
Purchase #5	$40.28	5.772%	$42.605	$42.61	$42.60	$42.60
Purchase #6	$101.36	4.248%	$105.6658	$105.67	$105.65	$105.70
Purchase #7	$12.56	4.316%	$13.1021	$13.10	$13.10	$13.10
7 purchase totals =	$559.63		$597.7185	$597.72	$597.65	$597.80