You can use a I2C or logic level shifter 

One side is 5V arduino other side outputs what every supply voltage you give it. In your case 7V

1488 and 1489 serial drivers should do the job.

I need to do some bit banging on my cars satellite radio module input/output jack. Unfortunately the radio communicates to the satellite radio module using 7.5 volts.  
Is there a circuit I could use to get my Arduino output pins to 7.5 volts?   
Its a serial communication with only 2 pins(not CAN bus).

7.5 volts output from Arduino pins