"Turning his little savingsbox about in his hand," Mr. Deasy tells Stephen, "These are handy things to have. . . . You just buy one of these machines. You'll find them very handy." Trolley conductors of the time made change with barrel-and-lever devices (still sold today) that could be clipped to their belts. They may be what Joyce has in mind, though they can hardly be called boxes.
The version shown in the photo is American, but it does have five barrels ("See. This is for sovereigns. This is for shillings. Sixpences, halfcrowns. And here crowns. See"). And the levers on such devices do eject coins ("He shot from it two crowns and two shillings"). But the narrative shows Mr. Deasy tapping his device "against his thumbnail," so perhaps Joyce has something smaller in mind.