You are right, there is no RoundUp(…) function in MDX for eazyBI. But MOD(…) function is available for you. The syntax is a bit different though - you specify the X and Y as the function parameters: MOD(X, Y). Try the following
X - MOD(X, 1) + 1
Note that there is also Fix(…) function available that would return the integer portion of the number (without rounding).