Is there a language technique that categories inverse meanings?

After being asked if I want a receipt at the markets, I notice I can alternate between - I'm good - I'm fine - I'm okay

All of these by literal meaning, vaguely motions a "positive" response, whilst they are used in a negative way, i.e. "No thanks"

What do we call this a type of language technique? If there is such a thing

The primary strategy here, in terms of pragmatic implicature, is

indirection

Instead of stating a bald negative 'no' which may be considered abrupt, the speaker is stating something positive. Since, if you wanted the item you'd say "Yes, thanks" or something similar, the fact that you said something else, like "I'm OK", the hearer can then infer that you mean something other than 'yes', and therefore, won't have to give you a receipt.