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	$80.30	12.717%	$90.5118	$90.51	$90.50	$90.50
Purchase #2	$54.92	3.654%	$56.9268	$56.93	$56.95	$56.90
Purchase #3	$134.47	6.801%	$143.6153	$143.62	$143.60	$143.60
Purchase #4	$175.96	3.708%	$182.4846	$182.48	$182.50	$182.50
Purchase #5	$162.25	7.293%	$174.0829	$174.08	$174.10	$174.10
Purchase #6	$75.54	12.372%	$84.8858	$84.89	$84.90	$84.90
Purchase #7	$225.97	7.509%	$242.9381	$242.94	$242.95	$242.90
7 purchase totals =	$909.41		$975.4453	$975.45	$975.50	$975.40