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	$208.42	13.454%	$236.4608	$236.46	$236.45	$236.50
Purchase #2	$40.67	3.441%	$42.0695	$42.07	$42.05	$42.10
Purchase #3	$60.46	8.331%	$65.4969	$65.50	$65.50	$65.50
Purchase #4	$217.59	9.636%	$238.557	$238.56	$238.55	$238.60
Purchase #5	$63.62	5.173%	$66.9111	$66.91	$66.90	$66.90
Purchase #6	$44.32	12.484%	$49.8529	$49.85	$49.85	$49.90
Purchase #7	$103.78	7.556%	$111.6216	$111.62	$111.60	$111.60
7 purchase totals =	$738.86		$810.9698	$810.97	$810.90	$811.10