If you get arrested in-game, and you have 500 SPAS-12 ammo, and 500 desert eagle ammo, you get only 30 ammunition back for both guns, and you still have to pay thousands of dollars for your weapons. What's worse, is the country rifle/sniper rifle, which gives you back 5 ammo max. One way to fix this would be to remove the limits, however, it could also be balanced in other ways.
For example, if you're a cop, you get to keep all your ammunition (when off-duty), or maybe, you can only retrieve the full amount of ammunition by buying your weapons back from the clerk.
Additionally, the limits of stored ammunition for certain weapons could be increased (shotgun, deagle, rifle, etc), so that you lose less when you get out of jail.