Raise exactly 4.2357 times the BB everytime. The dealer usually has quarters in his pocket so you can make change to the exact amount.
Seriously,
it depends. Unlike the somewhat homogeneous blend of players online, every live table is different.
Some tables a $20 UTG preflop raise will get 5 callers. And $15 to $25 raises are "normal". In the same room, with a different group of players, a $5 raise will fold everyone around to the blinds.
You will have to observe what others at the table tend to raise and note the results. When you raise, see who has a tendency to call and who autofolds.
Experiment with your raise amounts, and observe the different raise amounts of others, and note the different results.
Why are you raising? Because you have XY suited, and you are "suppose" to raise 3x+1.25 per limper? How about you are raising to isolate, or maybe you are raising to steal blinds, or are you raising for value? This reasons will dictate different amounts.
AND IT IS A LIVE GAME. If a guy yet to act is jumping up and down in his seat and grabbing for his chips, maybe you don't want to raise at all, maybe you want to limp and re-reraise (and the reraise should be exactly 3.8879x the original raise
).