Found in the wonderful www world...

- Don't care - generally quite negative, informal, and can be construed as impolite at times
- I don't mind - quite polite way of expressing you have no preference.
- It doesn't matter - can be used to dismiss a suggestion for example, or simply express that whichever option chosen is irrelevant.
- Never mind - can be used dismissively or when the information is no longer needed. can also be used when you're frustrated etc.