GY-521 MPU-6050 + Arduino nano - Logic converter or not?
According to 28.2 in the Atmega (the microcontrollers used on the Arduino nano) datasheet, it looks like Vih(input high voltage) is 0.7V-0.8V at minimum. So you probably don't need a converter for the INT pin (since that is an output for the MPU, but you'd need a converter for everything else (since both SDA and SCL are input/output for the MPU and the Atmega).

The ebay site says 3-5V for the main supply because it looks like it has a regulator on board. As for the IO lines themselves, it's hard to say if it has any converters on board. 

Atmega datasheet: http://www.atmel.com/Images/doc8161.pdf