I am rendering a Roblox character in Blender to make a GFX. I seem to be continuously running into this issue, no matter how many times I re-render the image. How do I fix this?
are you using a jpeg as the mouth's texture, or as render output?
Anyway, jpeg is a really harsh lossy picture format. There is always a quite noticeable loss with it.
I recommend you read the Blender Manual's page about the Supported Graphics Formats. Starting by this very simple yet quite true Hint:
If you are not interested in technical details, a good rule of thumb for selecting output formats for your project is:
if you intend to do compositing or color grading on these images.
if you intend on-screen output or encoding into multiple video formats.
for on-screen output where file size is a concern and quality loss is acceptable.
All these formats support compression which can be important when rendering out animations.
TL;DR : don't use jpeg if you care about quality.