C# Input.GetKey("Tab") Double Tap

Hi everyone, how do you check if a key has been tapped twice? I want to check if the tab key has been tapped once.If it has been tapped once I want to display a GUI.Box. If tab has been tapped twice I want the GUI.Box to go away.

if(Input.GetKey("Tab")){
GUILayout.Box("",GUILayout.Width(150), GUILayout.Height(35))
}

public class ToggleGUI : MonoBehaviour {

	private bool display = false;
	
	void Update() {
		if(Input.GetKeyDown(KeyCode.Tab))
			display = !display;
	}
		
	void OnGUI() {
	if (display)
		GUILayout.Box("",GUILayout.Width(150), GUILayout.Height(35));
	}

}