smell (notice/identify something by using your nose)
These verbs indicate that the perceiver is focusing on a specific object. They can be used in the progressive form.
He was looking at the trees in the garden when the telephone rang.
Judy is smelling the flowers Paul has given her for her birthday.
smell (have a particular smell )taste
These verbs indicate a perception in general. No progressive form.
She hears a noise.
They smell smoke.
These verbs indicate appearance. Non-progressive.
It smells strongly of fish.
The noise sounds like thunder.
'see' can sometimes be used in expressions in the progressive.
John is seeing the doctor.
When 'feel' is used to describe emotions, the progressive form is sometimes used.
I feel / am feeling great today.
I feel cold (physical feeling is normally non-progressive)
As to the progressive form the usage of 'smell' and 'taste' might differ, depending on whether it indicates an action or 'non-action'.