Greetings...

In the case of so called "Wikipedia reference-linktennis elbow" it is important to consider treatment beyond locally treating the elbow site as it is prone to recur. Check carpal gliding with wrist extension, pronation supination ROM etc... Look at the upper arm and shoulder during pronation / supination for compensations . If you consider repetitive tasks such as "checkout person", why is it that not everyone in this job develops tennis elbow ? Probably because of limitation elsewhere ie-lacks wrist extension... causes abonormal stress at the lateral elbow to compensate causing a chronically agitated extensor complex. If there is a history of a fall onto the same hand check for "pushed radius"syndrome etc... .

ie- look elsewhere .........cheers.....Thomas