The code definitions are as follows:
P0303 Engine misfire detected on cylinder #3
P0304 Engine misfire detected on cylinder #4
P0420 Catalytic converter efficiency below threshold
P0442 and P0445 indicate that the evaporative emissions system has detected a leak during a self test.
Diagnosing the causes of these codes does require some special test equipment, so you may want to take the vehicle in to your favorite repair shop to have the manufacturer's test routine for each of these codes performed to find the root cause of the problems before doing anything else.
If you for some reason do not want to take the vehicle in for a professional diagnosis, common causes for these various codes include:
(1) The misfire codes are often the result of worn ignition tune up parts including spark plugs and/ or plug wires.
(2) The catalyst efficiency code is stored because the catalytic converter is no longer operating properly. If you have been driving for some time with an intermittent engine misfire condition, the unburned fuel from the misfire that passes out of the engine and into the CAT is the likely cause of the failed CAT. Fix the misfire problem before having the cat replaced. You may want to call your local Dodge dealer to see if the catalytic converter on your vehicle is still covered under a federal emissions warranty (some models are covered for up to 8 years); if it is, they will replace the expensive catalytic converter for you for free.
(3) The evaporative emissions system leak codes are often caused by a leaking or improperly sealed gas cap.