I'm not sure I understand the question. There shouldn't be any loss...?
For example suppose you have eight players and a buy-in of $50, and you know everyone will bring 3 x $20.
Ahead of time, you could get $80 in $10 bills and put them in a box. As people buy in with their 3 twenties, you give them change of $10 each.
Once eight players have bought in and you've given them all change, there's 8 x 3 x $20 = $480 in the box, which is 8 x $50 plus your original $80.
At the end you cash out the $400 from the buy-ins, and you're left with $80 in twenties instead of tens.
So again: What loss?
Obviously this is a simplified example, but the point is that if you have a "float" of change at the start of the night, you should have the same amount left at the end of the night. If you don't, you're not making change, you're giving away free money!