Tasker: How can I close chrome when at a specific website?

You would need a plugin that enables you to interface with chrome (as chrome doesn't come with a way of other applications seeing the current web address built in), I couldn't find one with a brief search, but there may be one.

You could set it up so that when you open a specific link in chrome (either from the google search app, facebook, or another app), it scans the intent* for certain urls, and if it contains them, alerts you, if it doesn't, passes the intent on to chrome.

This may get you stuck in a loop (it tries to pass the intent on, but catches it again), so you could use a redirection service (i.e. you pass the intent on with something extra infront, so that it doesn't redetect it, and then chrome loads it, gets redirected to the original web address).

One final thought, you could use tasker to register to receive specific links (the same method that allows links to be opened in apps when you click on them, e.g. wikipedia).

Anyway, the following link should be useful, I figure you would like to work this out yourself, so I won't provide a step by step solution (unless you really want one): http://tasker.dinglisch.net/userguide/en/intents.html

*an intent is a message that is passed between application on android, for example, when you click on a link and it opens in your web browser, or you click on an address and it opens in mapps.