Make WebGL build look lower resolution

I'm working on a 3D webgl game and was wondering if anyone has any insight into rendering at a lower resolution without sacrificing canvas size. Basically, I'm making a 640 x 480 game that I would actually like to be 320 x 240 or somet$$anonymous$$ng to that nature so it looks pixelated, like Old School Runescape or t$$anonymous$$s game. T$$anonymous$$s is for aesthetic reasons as well as any performance it could save me. Thanks!