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	$11.53	9.123%	$12.5819	$12.58	$12.60	$12.60
Purchase #2	$99.86	13.870%	$113.7106	$113.71	$113.70	$113.70
Purchase #3	$182.59	4.540%	$190.8796	$190.88	$190.90	$190.90
Purchase #4	$122.88	12.190%	$137.8591	$137.86	$137.85	$137.90
Purchase #5	$162.84	7.126%	$174.444	$174.44	$174.45	$174.40
Purchase #6	$154.75	8.733%	$168.2643	$168.26	$168.25	$168.30
Purchase #7	$163.82	12.145%	$183.7159	$183.72	$183.70	$183.70
7 purchase totals =	$898.27		$981.4554	$981.45	$981.45	$981.50