When I used to use cash I used to do this all the time. I would nearly always overpay to minimise the number of coins in my pocket. For example I had a bill of £1.63 and I was paying with two £1 coins, I would get 37 pence in change, which would be a minimum of four coins (20p, 10p, 5p, 2p). So I would pay £2.13 to get a 50p or £2.03 to get two 20p coins.
95% of the time the person serving me would clock on to what I was doing but the other 6% it'd take some persuasion, and occasionally they would insist on giving me back my overpayment before ringing it up.
95% of the time the person serving me would clock on to what I was doing but the other 6% it'd take some persuasion, and occasionally they would insist on giving me back my overpayment before ringing it up.