Pretty much, you can't make a WinForms app respond well to different resolutions: it's possible, but it's a heavy amount of work and probably won't be too wonderful when you are finished.
The problem is that although all controls can be Anchored and Docked so they resize automatically, that doesn't have any effect on text within the controls: so you end up with a large button with tiny unreadable text in the middle, or a tiny button with huge unreadable text in the middle.
While it's possible to get round this by handling the Resize event for each control and working out what font size to use based on the new display area, that's not trivial and generally takes a fair amount of trial and error, plus the odd "fudge factor" thrown in to deal with strange cases.
You can do it, but it's serious work - WPF handles it a lot better!
The other solution is to redesign your UI to work well at multiple resolutions in the same way tat Visual Studio does: a central "work space" with all the tools in panels which float or dock round the edges. But for a POS system, that probably isn't practical!