You can use the ceil function: Mathematical function calls
The ceil() function should perform this rounding.
As Sebastiaan indicates, there is no way to do this automatically throughout your application. If this decimal is stored in an attribute, you could use a before commit event handler that changes the value of $Entity/Attribute to ceil($Entity/Attribute).
There is no option for this to handle it all automatically, the choices you have are to round numbers 'Half away from zero' or 'Half to the nearest even number' (also called bankers rounding)
Edit: For doing it manually, use the ceil function as others have mentioned.
Or file a feature request for more rounding modes.