I checked the Louisiana Confederate Soldier Burial Database at...

http://www.lascv.org/burial.htm

I found several men named Tucker listed but none that matched your ancestor. I suggest you also post this on the Mississippi in the Civil War Message Board at...

http://www.history-sites.com/mb/cw/mscwmb/

Finding gravesites is difficult. The best place to start is by talking to the oldest living descendent you can find and work your way down.