Okay... if I might make one suggestion... don't use ISO 100 unless you are in a seriously bright environment. Your camera will be nice and sharp with low noise at a much higher ISO than 100... You can safely count on ISO 800 and unless you plan on some serious sized photos 1600 will likely be none the worse for most things.
When you do shots at ISO 100 you are increasing the chances of camera shake unless you are on a tripod and are using a timer on the camera. Even if it is on a tripod, you pressing the shutter can cause it to shake a tiny bit.
Also are you going manual? Or did the camera choose these setting on P mode? I can't believe the camera would have picked those setting for the first photo, seems very underexposed.
I asked @gibson12 to shoot some shots on a tripod at ISO 100 at different apertures in response to his/her opinion on the sharpness of the lens based on the photo posted.
The first shot at f/1.8 is severely underexposed which doesn't make sense to me because the shot at f/4 is much better exposed at .6 seconds vs. 1/25 second at f/1.8. I can't really give any opinion on the first shot because of the underexposure. In the other shots it seems the camera was set up with a slight tilt where the top shelf seems in focus vs. the bottom shelf not. I'll have to download the photos and zoom in to get a better read on the sharpness.
To avoid any shake on a tripod you could use a remote shutter or a time delay shutter.