I asked the same thing in another thread, this is what I came up with and what I'm using now to start the next program.
Test the following TM, if Anchor is 105, test 107.5:
-you get 5 solid reps, great, it's your 85% TM
-you get 4 solid reps, keep the TM of the Anchor (105) for next cycle
-you get 3 solid reps, that's the 90% TM, adjust accordingly (drop 5% if you want 85%TM, keep it if you want 90%)
-you get 1-2 reps, you screwed up at some point by doing weeks/months with too high of a TM. Go back 2-3 cycles, eventually re-test the scaled TM if you want to make sure.
If the program you just did includes stuff like PR sets, Jokers or "work up to TM for X number of reps" you most likely already have a very solid feedback about your TM and numbers in general.
I.e. if you had a 105kg TM and a 95% 1+ PR set week where you got 7 reps @ 100kg, you can be fairly confident you won't have issues hitting 107.5 x5.