The rule that takes care of the packets after the first `ACK` is:

 iptables -A OUTPUT -m state --state ESTABLISHED,RELATED -j ACCEPT

It essentially means: let all packets that are part of, or related to, an established session go through. All packets from your machine that follow the initial `SYN` (provided there was a valid reply to that) are part of an established session, so they will pass. 
(`RELATED` is used for protovols like FTP, if you have that module enabled, where a "normal" session can involve more than one TCP session.)

Note that since you've set up DNS redirection to Tor too, and use `AutomapHostsOnResolve`, the IP address your browser (and other software) will see are not www.example.com's IP address but a virtual address in the range you specified (`10.192.0.0/10`).