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	$78.48	6.495%	$83.5773	$83.58	$83.60	$83.60
Purchase #2	$72.76	8.126%	$78.6725	$78.67	$78.65	$78.70
Purchase #3	$71.71	12.402%	$80.6035	$80.60	$80.60	$80.60
Purchase #4	$5.40	5.405%	$5.6919	$5.69	$5.70	$5.70
Purchase #5	$107.50	4.531%	$112.3708	$112.37	$112.35	$112.40
Purchase #6	$38.25	5.737%	$40.4444	$40.44	$40.45	$40.40
Purchase #7	$242.59	7.405%	$260.5538	$260.55	$260.55	$260.60
7 purchase totals =	$616.69		$661.9142	$661.90	$661.90	$662.00