He cannot force you if this is implemented well. Asking to see reveal a vote should of course be illegal. But more importantly there should be a randomized incentive who should keep their receipt and who should not.
At the voting station at the exit there could be a pick-one-ball-out-of-ten type "lottery" (implemented in any way as long as it's somewhat fair: Roll a dice, bingo machine, pick something with your eyes closed, whatever..). Then if you happened to get the one white ball amongst the nine black you get to keep the receipt, otherwise you throw it in the incinerator/shredder.
The point is you actually only need a small percentage of the receipts to prove if the voting machines are faulty. If you have 100 random receipts from a total of 1000 votes, only 10 votes can be tampered with before you expect tampered votes to show up among the receits. 10% receips will thus "guarantee" a maximum of 1% tampered votes. If you are more paranoid you keep 50% receipts and get a maximum of 2 out of 1000 tampered votes before you expect to find them. (0,2% tampered votes)
In any case you tell your boss you got the black ball and had to shred the receipt.