A test like this is possible:
15
0 35
12000000
12000000
-1

First time it occurs in Test 9.
This means that you should pay the same tax for any amount of salary. It is ok to output 0.00 for all such tests, despite it is not correct always because of interim roundings of regional coefficient.
Everything else is well-described in previous comments, basically correct numbers round and correct searching of initial salary (you should search for max possible value with 2 decimal places in it) are the only things that can make the initial problem description being unclear.