Back in the old days when I learned to create web pages, the rule of thumb was: Don't resize your images with HTML/CSS, provide the image in its "native" resolution. Otherwise, it will be upscaled or downscaled by the browser and the image will look blurry or ugly.
Those were the days when we didn't have high-resolution tablets, huge screens and browsers with built-in zoom functionality using smart algorithms.
My gut feeling tells me that a lot of people don't have their browser at a zoom factor of 100%, so browser-side scaling is going to happen anyway -- providing a high-resolution source should lead to a strictly better result than the native-for-100%-version in that case. Have we reached the time yet where it makes sense to provide images with higher resolution¹ than required when designing new web sites?
¹ ...within reasonable limits considering the users' bandwidth, of course.