I would say you are safe.
At face value, an ISP cannot sniff packets properly if you are going through Tor because it is encrypted with onion technology. When you connect to the Tor network, it works like this:
- you make a request to a website in your Tor-enabled browser
- that request is encrypted three times and sent from your computer to the ISP and then to the first server in a long chain of servers (usually 15-20 or more)
- the ISP only sees encrypted packets (they cannot read) sent to and from that first server in the network which is a relay server and not hosting any content to see (besides encrypted packets)
- as the packets are sent to each server, a layer of encryption is removed and another added and the last three servers remove the encryption entirely (one by one) so that in the end, the last server can see only as far back as the previous server.
However, you should avoid logging into any personal accounts through Tor since anything you connect to can all be seen by the exit node and it would completely disrupt the whole purpose of using Tor. Additionally, an exit node can track patterns and could ostensibly figure out who you are if you are a heavy user of the same node, so it's good to constantly change "identities".