A similar approach can be taken in Photoshop, but here is one solution done in Illustrator:
1) Draw rectangle

2) Select rectangle > Effect > Stylize > Rounded Corners > ~10px

3) Select Direction Arrow (a) > Grab top right corner of rectangle holding shift
to keep structure and create your desired angle

4) Select rectangle > Object > Expand Appearance
--This will make the stylized rounded corners actual points that will be used for the outline

5) Duplicate this rectangle
(cmd+copy, cmd+f to paste in front)> Object > Transform > Reflect > Horizontal
-- set aside for now.

6) Draw new rectangle
7) Place new rectangle over original rounded corner rectangle, aligning baseline of both rectangles

8) Select both rectangles > Pathfinder > Minus Back
-- (ignore 2nd rectangle on top, shouldn't have included it in this screenshot)

9) Align 2nd rounded rectangle to baseline edge.

10) Select all > Pathfinder > Divide
-- This will allow you to delete the excess area

11) Select all > Pathfinder > Merge

Obviously, this is not the best solution for everyone, but it should help you wrap your head around at least one way to achieve this result. I often just need someone to get me started down a path to a solution. Hopefully this does that for you.