Search Queries, an analysis tool that visualizes your site's presence in our search results. It has two main parts: an interactive graph, and a table containing detailed data related to queries for which your site appears in our search results. Two of the most important pieces of information in the table are "impressions" and "clicks."
Google Webmaster Blog announced a "slight change" to how the search queries reports are displayed. To simplify their interpretation. Instead of showing numbers rounded to two or three digits, the numbers will now be shown with one or two significant digits.
What does that mean? For e.g, instead of Webmaster Tools showing you 246,000 impressions, it'll now show 250,000 impressions, which is a nicer representation for a better, less confusing experience. Google says this is "a nicer representation for a better, less confusing experience." And, that they "haven't altered the way we calculate the numbers internally, but only changed how we round them in Webmaster Tools."
Generally, a difference of less than 10% between the numbers you see now and those you saw prior to this change should not be considered significant.
Here is a before and after screen shot. The numbers on the left are the old numbers and the numbers on the right are how those will be rounded going forward.