What formula would I used to calcuate a future date and if it lands on
a weekend to "round up" the future date to the following Monday (or
round down the Friday)

If the future date is in A1, here's one way to round up weekends to Monday:
=A1+IF(WEEKDAY(A1,2)5,8-WEEKDAY(A1,2),0)

And to round down to Friday:
=A1-MAX(0,WEEKDAY(A1,2)-5)