Robinson Crusoe

If I have to halve something, do I round up or down?

It depends
The instruction that tells you to halve something will always tell you whether to round up or down. BUT note that some cards say "Lose half of X, rounding down". In this case, read it literally: it is the LOST part that is rounded down, i.e. you lose less than you otherwise would -- it is rounded in your favour!