Add a zero when there is only 1 decimal

Question

Good staff, I have a system for issuing electronic invoice, there is a government rule where the values of duplicates(installments) must possess exact 2 decimal places. I use number_format to declare that it shows only two decimal places, but when the number is an integer decimal it does not show a zero, example:

Installment 1 : R$ 140,11 Installment 2: R$ 140,10

What happens is that when shows the plot 2 it shows me R $ 140,1 , IE, eats a zero, someone would know me how to add this zero when it happens this case?

I use it to show two decimal places:

number_format($calcula_duplicata, 2, '.', '');