Should SMD footprints be rounded?

Yes, SMD footprints should have rounded corners as per IPC-7351A

Corner radius is 25% of the shorter side of the pad but not more than 0.25mm (10mil which is not exactly the same but close enough here)

Why? The corners do not add anything useful (no additional adhesion, no additional stability or conductivity). But on reflow soldering the solder does not always flow into every corner possibly leaving copper exposed. Additionally: it's better to have stencils with rounded corners.

The only reason for pads with edges was that some tools did not support rounded edges.

Addition: no, pads with reasonably rounded corners do not have to be bigger because the corners didn't add anything useful to begin with.

per IPC-7351B standard:

Also, the usage of oblong, or rounded, land pattern pads is considered advantageous for lead free soldering processes in comparison with rectangular pads, as the oblong shape provides for a pull of the solder on the pad. An exception to this rule occurs when the heel portion of the land pattern has to be trimmed due to the component body standoff being less than the paste mask stencil thickness or the heel having to be trimmed due to “Thermal Pad” interference. In these two cases, the rectangular pad shape is preferred to compensate for the reduction in copper area of the land pattern pad length.