The ornamental design for a mobile cashregister, as shown and described.
FIG. 1 is a front View of a mobile cash register;
FIG. 2 is a rear View thereof;
FIG. 3 is a bottom View thereof;
FIG. 4 is a top plan View thereof;
FIG. 5 is a right side View thereof;
FIG. 6 is a left side View thereof;
FIG. 7 is a perspective front View thereof;
FIG. 8 is a perspective rear View thereof;
FIG. 9 is a perspective front View of the mobile cash register in use, wherein the mobile cash register is slid open and the camera at the back side is exposed; and,
FIG. 10 is a perspective rear View of the mobile cash register in use, wherein the mobile cash register is slid open.