Yes. Assuming you're talking about CRT monitors, the monitor takes up a large percentage of the total power consumed by the computer system, from something like 60 Watts for a small monitor to more than 100W for a large one.
However, frequently switching on and off puts a lot of stress on certain components inside the monitor and may shorten its life.
All modern monitors are made capable of going into a standby mode where they consume only a small amount of power when the computer has not received a fresh command from the user for some time. This is done when you set the power options in Windows.
Whether it's worth switching off for 5 or 10 minutes depends on how often you do it. If you leave it only a couple of times a day, the saving in electricity will be quite small and IMO not worth the extra stress on your monitor. Better to set the power settings properly.