Is Jupiter's rotation slowing? According to Wikipedia, re Europa's tidal flexing:


  the tidal flexing kneads Europa's interior and gives it a source of
  heat, possibly allowing its ocean to stay liquid while driving
  subsurface geological processes.The ultimate source of this energy is
  Jupiter's rotation, which is tapped by Io through the tides it raises
  on Jupiter and is transferred to Europa and Ganymede by the orbital
  resonance.


https://en.wikipedia.org/wiki/Europa_(moon)

Does this imply that Jupiter's rotation is slowing over time, since it is losing energy due to raising tides on Io?  (Or just generally, does raising tides cause rotation to slow?)
Yes

Tidal locking is a mutual process, and both the satellite and the parent body will eventually 
permanently face each other. However, while tidal locking of a satellite can happen relatively quickly (that is, within the life span of the solar system), tidal locking of the parent body is extremely slow and will in a practical sense never happen (the current age of the universe is not enough in most cases).

The relative mass of the satellite and the parent body is one of the most important factors:


Charon and Pluto with a mass ratio of just 8.1 are already mutually locked.
The Moon and Earth has a relatively high mass ratio of 81. This causes a measurable effect on the Earth.


Compare that to the mass ratio of Juptier and Europa of 39,600 (or Io: 21300, Ganymede 12,800, Callisto: 17,600). While the time required for a locking of Jupiter itself is difficult to measure due to the fact that we don't have the necessary data about the moons, this is not a noticeable effect before the Sun dies.

Tidal locking of the parent body can most likely be justified by conservation of energy, but conservation of momentum gives a more intuitive view: As the satellite slows down and moves away from the parent body, its angular momentum increases (angular momentum is proportional to distance times velocity, and the orbital velocity is proportional to the square root of distance). This angular momentum must be supplied from somewhere. The only source for that is the rotation of the parent body. Even if all the moons of Jupiter were to completely escape, the angular momentum drain is not enough to stop the rotation of Jupiter.