Your assumption that as long as you are totally honest, you've got nothing to worry about would be reasonable if polygraphy were truly as accurate and its practitioners claim. But the truth of the matter is that polygraph "testing" has no scientific basis and results in many truthful persons being falsely accused of deception and wrongly disqualified from employment.

Whether or not to use countermeasures is a personal choice that neither I nor anyone else can make for you. But I suggest that before making this choice, you educate yourself about polygraphy. A good starting point would be to read The Lie Behind the Lie Detector.

Regarding the risk of being detected using countermeasures, you should be aware that not using them is no guarantee that you won't be falsely accused of such. Countermeasure detection (like lie detection itself) is largely an exercise in guesswork and badgering the subject for an admission. For additional discussion, see the message thread, Counter-countermeasure Techniques.

I can tell you that if I had my own pre-employment polygraph examinations to do over again (see my statement, "Too Hot of a Potato: A Citizen Soldier's Encounter with the Polygraph") I would most certainly use the kinds of proven countermeasures detailed in TLBTLD rather than naively counting on my honesty alone to pass.

Yeah, unfortunately "just telling the truth" doesn't really cut it. I was nervous about countermeasures too -- the only thing I was really comfortable trying were mental techniques -- i.e. imagining something like falling off a cliff to hopefully induce some kind of response for the control questions...