Remember, sharpness is very much in the eyes of the beholder; an image which another judges to be "sharp" may be unacceptable in your eyes.... or vice-versa!
When it comes to the crunch, you only need "sharpness" which will stand up for your purposes. If all you're ever going to do with your photos is view them on a computer monitor, you can probably get away with substantially less overall quality than if printing them to poster size.
A low-cost, low-quality 1.3 Megapixel digital camera may fulfil your needs quite adequately. If your requirements are very demanding (or you simply want the best), a top-end 10 Megapixel professional SLR digital camera may be the only camera which will do the job.
The one thing I can't tell you is exactly what your needs are!
To sum up:
Use a smaller lens Aperture when possible (most important in close-up
work).
Use a short (fast) Shutter Speed when possible.
Use plenty of light on your subject (aids both the above).
Use a tripod / support if practical; otherwise try to brace your hands
when shooting.
This little lesson has of course only scratched the surface about "sharpness". One of the huge advantages digital has over film is that it allows you, the photographer, to experiment as much as you wish at virtually nil cost (unless you choose to print your photos). I encourage you to get your camera out and take many shots at different shutter speeds, different apertures and so on, just to see exactly what results are produced by using different settings.
When taking such "test" photos, just make sure your camera is absolutely rock-steady, for the slightest vibration - even at fast shutter speeds - can take the edge off sharpness.
Good shooting.