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	$208.37	4.270%	$217.2674	$217.27	$217.25	$217.30
Purchase #2	$234.27	6.439%	$249.3546	$249.35	$249.35	$249.40
Purchase #3	$180.85	13.291%	$204.8868	$204.89	$204.90	$204.90
Purchase #4	$152.32	12.338%	$171.1132	$171.11	$171.10	$171.10
Purchase #5	$139.55	13.565%	$158.48	$158.48	$158.50	$158.50
Purchase #6	$20.91	3.769%	$21.6981	$21.70	$21.70	$21.70
Purchase #7	$117.83	12.527%	$132.5906	$132.59	$132.60	$132.60
7 purchase totals =	$1,054.10		$1,155.3907	$1,155.39	$1,155.40	$1,155.50