Three spraying machines working together can finish painting a house in 60 minutes.

Let the time taken by 5 spraying machines to finish a painting job be x minutes.

Since the number of spraying machines and the time taken by them to finish a painting job are in inverse variation, we have:

$3 \times 60=5 \times x$

$\Rightarrow 180=5 x$

$\Rightarrow x=\frac{180}{5}$

$=36$

Thus, the required time will be 36 minutes.