try like below.
Towords(truncate(6400.75), 0) + " Rupees and " + towords(abs(100 * (truncate(6400.75)- 6400.75)), 0) + "Paise";
result is: six thousand four hundred Rupees and seventy five paise
The first part i.e.
returns 6400, and will ignore the decimal place.
Second part i.e.
(abs(100 * (6400.75 - truncate(6400.75))
converts it to a positive value and multiplies the value to be non decimal.
If you have more decimal places you'll have to adjust the 100 multiplier.
hope it helps.