Hi there,
If you already have a micro controller chip that is to be used for this project and you happen to have an available output pin, then you can simply use that pin to drive a small transistor and that transistor drive a small inductor and with a Schottky diode you have a boost converter that should easily boost 3v up to 5v no problem with a set duty cycle.
An unregulated boost converter is a lot easier to build then a regulated one so you're getting off easy here
Parts List:
1k resistor
2N2222A transistor (or whatever you have around)
Small inductor (100uH or higher for say 50kHz operation)
Small Schottky diode like 1N5817 or even smaller
Small electrolytic output cap
Probably set the duty cycle to around 50 percent maybe with some cutback when the voltage rises or use a zener perhaps, keeping the input to the booster at 3.3v while supplying 5v to the other parts of the circuit.
As the voltage starts out at 3.3v the booster will start creating a higher voltage, which should reach at least 5v rather quickly.
The required power pin may have to be diode OR'd to accept the new voltage (bootstrapped) if you need to drive the uC at 5v too.