More than one to a sheet
Choose a paper size in the PDF export and a second option appears: print more than one to a sheet. The design is repeated as many times as fits, and the panel tells you how many before you export.
It counts the bleed
What gets tiled is the design plus its bleed, because the bleed is printed and then cut away. A 5 × 7 in card with 0.125 in of bleed occupies 5.25 × 7.25 in, and that is the number the sheet is divided by.
It turns copies where that fits more
Two 5 × 7 cards do not fit upright on Letter — side by side they want 10.5 in across an 8.5 in page. Turned a quarter turn they fit. The export tries both ways round and takes whichever holds more.
Trim marks are reserved once, at the sheet edge
Marks need a clear margin, but only where the sheet ends. Where two copies meet in the middle a mark runs into its neighbour's bleed, which is cut off anyway.
This is worth stating because the obvious implementation gets it wrong: reserve a quarter inch around every copy and a pair of 5 × 7 cards wants 11.5 in of an 11 in sheet, so you are told one fits when two do. The print layout calculator on this site runs the same function, so it gives the same answer.
What it does not do
It repeats one design. Several different designs on a single sheet is a different job — make one design the size of the paper and place each item on it as its own element.