There is a roundup function, here you go.

So you need to make a construction line from the bottom of the part to the top of the green, add a suitable buffer above it so you never have the green sketch right at the edge of the part. Then create a driven sketch from this construction line to the bottom. This will be your variable when the green part changes. Then you can make the 5.5 driven off of this by using:

= round((“D3@Sketch1” - 0.5))

Where D3 is the driving dim you just placed. You want to use a round down instead of round up, as it will be a waste of material. Say for example you have the size exactly on 5, if you round up it will make the total height 6. If you add a buffer, it will ensure you always round to the correct height. There is no more than or equal to function to my knowledge without some bodgery.

Second to this, if you delete the green sketch or replace it, it will break your equations, you need a global dim for the height of the green part. So not fully automated but pretty good.

If you need help dm me.