I would think the rfid library would be able to read multiple cards in a row... however I'm not familiar with it.

Here is an answer from a similar question about how to initiate a hardware reset with software using the watchdog timer - http://arduino.stackexchange.com/a/1478/31106 :

The SoftReset library makes it easy. Although it is not difficult to implement directly. Shown below..

#include <avr/wdt.h>
...
setup() {

  ...
  MCUSR = 0;  // clear out any flags of prior resets.
  ...

then when desired...

...
wdt_enable(WDTO_15MS); // turn on the WatchDog and don't stroke it.
for(;;) { 
  // do nothing and wait for the eventual...
} 
...

I would think the rfid library would be able to read multiple cards in a row... however I'm not familiar with it.

Here is an answer from a similar question about how to initiate a hardware reset with software using the watchdog timer - https://arduino.stackexchange.com/a/1478/31106 :

The SoftReset library makes it easy. Although it is not difficult to implement directly. Shown below..

#include <avr/wdt.h>
...
setup() {

  ...
  MCUSR = 0;  // clear out any flags of prior resets.
  ...

then when desired...

...
wdt_enable(WDTO_15MS); // turn on the WatchDog and don't stroke it.
for(;;) { 
  // do nothing and wait for the eventual...
} 
...