The ornamental design for a cap for dispensingtube, as shown and described.
FIG. 1 is a bottom, left, frontal perspective view of our invention;
FIG. 2 is a top, left, frontal perspective view thereof; and
FIG. 3 is a front, rear, left side, and right side elevational view thereof;
FIG. 4 is a top plan view thereof; and,
FIG. 5 is a bottom plan view thereof.
The broken line representations of threads and other internal structures in FIGS. 2 and 4, a lower closure end of FIGS. 1 and 5 are for purposes of illustration only and form no part of the claimed subject matter.