How much wear do you have between pads and discs?
Sometimes when both are worn down, and the piston is approaching the end of it's travel, the piston struggles to withdraw away from the disc after braking and will drag slightly on the disc, this can give you a squeal when driving normally.
Copper slip on the contact points between pads and calipers will alleviate the squeal but it will mask the problem rather than cure it. If you're approaching the point where discs and/or pads need changing then I'd do it now. If you take it to a garage they will usually do that sucking air through the teeth thing and say 'brakes are dragging mate you need new calipers'. Horseshit! Change discs and pads and you'll more than likely fix it!
I speak from experience with other cars however not necessarily Jeeps, but it's the same principle!