My biggest determinate tomato bush has curling leaves at the extreme
edges of some branches. The ones at some tips are curling into
balls--but are still very green and supple. Also new branches are
curled under themselves. I've got a indeterminate vine right next to
it, they have grown into eachother a bit. I didn't pinch enough and it
is
bushy for the first 18". It is having no problem, but is taller and
not as thick. Also gets a little less sun.
You don't say if you've checked into the interior of any of the
curled-up leaves: could be insects, like aphids.
Should have said that. I have checked under and down the stems from
them. Nothing that I could spot. It seems to happen at the most
extreme ends--tips of branches reaching farthest out fromthe cage or
on top. That made me think heat/sun was beating them up the most. But
more water didn't seem to improve it any. Only one of my plants have
wilted on me in the heat, so if anything I would think I was
overwatering not under.

I have one of those simple moisture meters and it was still moist (5
on a 10 scale) six inches down. So I held back water despite another
hot day. I came home late so I don't know how it faired. If it wilts
at least I'll feel better about drowning it more.

Really the plant looks spectacular except for the curling. I'm just
trying to right what is wrong since it is growing its fruit now.

A few more things you might look into:Tomato russet mites. These aren't
visible without magnification, even a 10x hand lens might not be
adequate to see them. The lower leaves and stems on affected plants turn
brownish or bronze color, with discoloration spreading upward. Also
various viruses, wilts, root rots and blights affect tomatoes, some of
which can cause curling. Also tomato leafroll, with leaves rolling
upwards. This is generally due to cold, wet soil condition (generally
seen early in the season.) I'd just keep watching it to see if any other
symptoms develop.