Convert decimal into Whole Number

[subjoin50]

I have a calculated column with long decimal numbers (col3). I want to change it into a whole number (like in col4) so that I can apply LOOKUPVALUE function to pull a column form another table. When I change data type to "Whole Number" or apply ROUND function to 0 digits (sometime ROUND function throw error saying greater than 64 bit integer) , visually decimal value changes to whole number but it still acts like a decimal number. How can I convert decimal number into a whole number and make it acts like a regular whole number? 

 Note: The solution has to be either in DAX or in Data Mode table not in Power Query. Any help will be appreciated!

[Greg_Deckler]

@subjoin50 

col4 = ROUND([Col3],0)