Funky Results with Parallel Resistors?

I did a practical in which we used nichrome wire as a resistor and used 1 then 2 then 3 and so on until 5 in parallel. Measured the voltage from one side of the top resistor to the other and measured the amps at the end of the circuit. Volts decreased with addition of wires and amps increased. The total resistance also (presumably) decreased. However when graphed on a V-I graph we get a curve, not a straight line though I believe this is meant to be ohmic resistance which has a straight line. Suggestions? Ty all :)