Trying to develop a rounding system that would always round up to the nearest x (50 for example) unless it was a multiple of 50

In a couple of mins I had 3 different solutions and identified the fastest.... yet the dev who it was for still couldnt grasp how it was done

best solution I had:

If you're always rounding up then that's by far the quickest way.

if x = 50 then return = 50.

if x = 51 then return = 51 + 50 - (51 modulo 50)

i.e. 101 - 1 = 100.

thought so, also allows for passing a bit in an enum of rounding state (forceup/forcedown/default) then can extend into the realms of the if block there