5 euros doesn't seem much for a pot of tea in Vienna I'm afraid.
I go to VIE around 3 or 4 times a year and tipping is not standard in Austria, but a small rounding up is - even students do this! Most restaurants include tax and service separately on the bill. This aggressiveness / rudeness seems to be on the increase.
i feel both conflicted and guilty about 'americanizing' the tipping culture here in europe -- tipping up to my normal norms because:
(1) its a very small amount anyway
(2) often the rest of my meal is already comped
(3) im used to it from personal background
and once in a while am gently rebuked by colleagues not to do so