I work in a similar way (though I normally pay for things under a fiver or so in cash). And I know I'll never pay interest on my card - after being stiffed for ten quid or so by being on holiday and missing the payment date by one weekend, I got a direct debit on it. The card company provides full-balance direct debit if you ask for it, but they only promote the minimum-payment DD.

Last time I went to the USA, I had $10 in change left over from the previous trip. I had to make an effort to spend that much cash in the month I was there!