The ornamental design for a toilettissueholder, as shown and described.
FIG. 1 is a top, front, and left side perspective view of a toilet tissue holder showing my new design, with the broken-line disclosure of both a moist wipes dispenser housed in the toilet tissue holder and an air freshener recess mounted at the bottom are understood to be part of the article in which the claimed design is embodied, but which form no part of the claimed design;