Got cut with a dirty blade desinfected with KMnO4.No local signs of inflamation. Last date of tetanus shot 17.11.2005. Shoul get tetanus shot again?

Yes. Since it has been more than 5 years since your last booster, you should get one even though there are no signs of infection/inflammation. Make sure that you get a Tdap, as we now know you need pertussis boost as well and you would not have gotten that back in 2005.
Get tetanus shot. It is o.k. that no signs of in fection but you are in incubation period and to protect yourself from tetanus ,better to get tetanus shot.Your last shot was more than8 years back ,by now you may not have good protection level against tetanus .