Just an FYI. I make tenon joinery with a router and table saw. The tenons are made on the router and have rounded ends. The tenons are cut on the table saw and are rectangular. The extra space inside the mortises gives the glue squeeze out some place to go. However, there is no reason that the tenon cannot be rounded on the end also
Round tenons and mortises are common in timber frame joinery as well as rustic and fine furniture. For example, the Welsh Stick Chair.
Best regards,
Allen