5 input 5 output MIMO pid tuning

hello, I have a system in state space form. It is stable in open loop.It is a 5 input 5 output MIMO system, with PID or PI. And it is in discrete form. How can I tune the controller? I tried the decoupling and to use looptune, but the response "spikes" as the error goes to+/- 0.001 (which in my system is not coincident with any particular thing).Is it a problem of integral windup? how can i solve it?

thanks so much

[Arkadiy Turevskiy]

It is impossible to answer a question that lacks specifics. Can you attach your model and clearly define the requirements for the controller?