Have One's Hand In The Till Meaning

(idiomatic) To embezzle, to steal from one's place of business.

Example: 1990, House of Cards, Season 1, Episode 1:
  Francis Urquhart: You've been a bit of a bad lad, haven't you, Roger?
Roger O'Neill: What?
FU: You've had your hand in the till.
RO: Francis, you're joking!
FU: Your expenses are paid by Central Office, aren't they? But you've been claiming quite large sums from the advertising agency as well. It's a bit naughty, Roger.