I have recently stopped informing ATC of the new heading when given an instruction to turn a number of degrees, on the basis that they can see it on the Mode S readout and I don't see the point in clogging the airwaves. Fair enough?
But I would never round up or down a specific heading instruction. In the majority of situations it might not matter, but occasionally it might and anyway I'm lazy - lying would involve having to reach up and change the heading bug on the MCP!