What browser do you use? Do you use browser zoom? Do you have a retina display? What is your OS/OS version?
We’ve tested your case on a several different machines with all major browsers and everywhere everything was pixel perfect. However, since we use percentage values to define size of the product grid there might be some imperfections here and there, e.g. if you have zoomed out/in your pages. In the general case browsers will try to round pixel calculation to integer (number without decimals), but sometimes there are misses.
Using a 4k monitor will surely help you see a more perfect web