Money can often cause problems in relationships. It's just an awkward and touchy subject. It's easy to feel like you're getting taken advantage of or suddenly realize six months after the fact that you forgot to pay them back for the movie ticket they bought you. I hate those kinds of situations.
A friend of mine called me the other day because she was running to the store to purchase an item that had unexpectedly gone on sale and she knew I was interested in one too. She offered to pick one up for me. A few hours later, I got an email from her telling me the exact cost, including tax.
I logged onto my bank's website, plugged in her address and the amount, and sent a check off to her, then an email to her telling her I'd done so.
I didn't have to think about it again (or try to remember to have my checkbook on hand the next time I saw her), she didn't have the awkwardness of wondering if she should remind me or just eat the cost, and neither of us had to wonder if we'd paid more or less than we ought to have. It was so lovely and I've had this experience with this same friend a number of times. She knows I'll pay her back in full and I know she'll be upfront about how much I owe her so I don't have to feel guilty.
I've really come to appreciate this from my in-laws. Bart's mom is the kind to be very upfront about money - you always know when they are planning to pay for dinner (no uncomfortable moments when the check arrives). There's no rounding up or down. If she owes you money for something you purchased in her behalf, you'll get reimbursed to the penny. And then when you pay her back, you don't have to wonder if you should round up. Easy and straight forward.
For someone like me who has enough social worries, this is very comforting to me. And I can't tell you how many times in the six years we've been together that Bart has commented how much he loves this about his mom. He probably mentions it at least once a month.
I'm sure you've all had "friends" who are happy to take advantage of you as far as money is concerned - never paying you back, or happily pocketing a little extra that you've paid.
Of course, I want to be the kind of person who doesn't drop a friend over $5, but even more so, I want to be the kind of friend that someone else doesn't have to worry will try and short them $5 (or $50).