How do I get my coworker to start either paying for stamps he asks me for or stop asking me for them?

A few months ago, my coworker asked me for two stamps. I told him I keep them at work, and I gave them to him. He did not offer the money to me, and so I was thinking “ok I won’t ask him for it because it’s only 88 cents.” About a week after that, he asked me for another, and I gave it to him. At that point I was thinking if he asks me again, I’ll tell him I took the stamps home. He did not ask until yesterday.

He asked for a stamp, I got a little flustered and was going to lie and say I took them home, but the lie would have sounded fake, so I said ok. He did not offer the money, and again, I did not want to sound cheap and say “that’s 44 cents, please.”

Is this something I should let go repeatedly, or what is a good way to ask for the money (honestly, I don’t want to sound cheap but it does add up).

Just FYI: We’re not anything other than work friends, we don’t hang out together, go to lunch or anything like that. We chat but nothing more, and our cubicles are next to each other.