I can round a number up to the next digit, the next ten or the next 100 or
the next 1000 ... but not to the next 500 .... in a spreadsheet in use for
estimating quotes for heating installations - anyone any ideas?

(Practical application is:- clips for holding underfloor heating pipe in
place - 1 per meter, but they come in boxes of 500, so if there is 2310
meters of pipe going to a job, that needs 5 boxes of 500 ... )