design – What is the best approach to have user input whole number values while hiding the fractional part?

Our financial web application deals with the currency values where the user inputs some change value either in whole number(USD 5) / fractions (USD 5.99). This change value sometimes gets auto calculated by the system in different scenarios and may results in fractional values because of the underlying calculation.

Although, our whole calculation is done on the actual decimal numbers our users wants us to be able to show only whole numbers and allow input in whole numbers only.

We can restrict the input element to take only whole number values but it is the system values that gets calculated but sometimes lead fractions part to be appended (which is expected because the underlying system has some formulas involving arithmetic calculations).

Even if we hide the fractional part it would be wrong at the user part to assume that there was never a fraction part but it was always there. Thinking that there is no fraction part, a user can give the wrong input value and have incorrect output.

Is there any optimum design we should take to show fractions separately while taking input as only whole numbers?