Set formula to 2 decimal places?

Hi All,

I’ve got a couple of hour columns, with a formula that is:
HOURS_DIFF({Stop Time},{Start Time})
which currently displays the difference as HH:MM, however this cannot have a SUM at the bottom of the column, or be used in any charts etc - so I’ve also added a second formula column which shows:

IF({Stop Time} = "", "00", SUM(ROUNDDOWN(SUBSTITUTE({Duration HH:MM},":","."),0),DIVIDE(SUBSTITUTE({Duration HH:MM},":",".")-ROUNDDOWN(SUBSTITUTE({Duration HH:MM},":","."),0),0.6)))

The trouble is this is showing 3 decimal places as the output → 5.217. how can I get this to round up to 5.22 - I tried adding roundup(CODE,2) to the code above but that just failed with a red !

Also, the IF statement is meant to look at the Stop Time column and if its empty, set it to 00, if its not then show the calculation, however it doesn’t seem to work - I’m getting a red ! in the field when the Stop Time is empty.

Any ideas on either of these please?