The connection is encrypted end-to-end and there is no need for SSL in that case.
Oh, didn't know that. So, is ChipMixer's server essentially the exit node?
It makes them a server pointing to tor.
I'd add onto what ranochingo said because as well as end to end encryption, there's encryption at each hop. Tor used to tell you the number of hops it did (and it used to be 6) each of these would be encrypted and the transit nodes are only able to see the last hop and next hop locations, the encrypted data and nothing else.
The basis of tor imo is Firefox so there's a chance different algorithms might be used.
simple example of encryption If you can't think of a way this can work, I'd explain it this way:
You transport the number 20, node 2 said their key was 5216 and node one said theirs was 5789 with the end server securely sending the code 562163
You could then transport your 20 in the following steps:
Send the sum of all keys to node 1: 573188
Node 1 subtracts 5789: 567,399
Node 1 sends this new number to node 2
Node 2 then does the same step and gets: 562,183
Node 2 then forwards to the service and the service finally gets: 20
Keys are much more securely sent than this, this is just an easy to explain example.