As Rygor said,
Tatiana is pronounced exactly as it's spelled, save for the
ia which is hard to explain to English-speakers, because it does not exist in English.
ia is a combination of a very short
i as in "sit" and a very short
a.
Now, for the specifics of Russian accents. The second
t (the one before
ia) is pronounced very mildly, and combined with the
ia, it might sound like a "ch" or "sh" to unaccustomed ears. So, to your question -
Tatiana is pronounced with a very mild "t", that might sound like "ch" or "sh" to non-Russians :)