What is the value of a 1940 US nickel?

Updated1940 is not a rare date for Jefferson nickels. Look on the back of the coin to see if there's a small mint mark letter to the right of Monticello. It may be blank or there may be a D or S.

Numismedia lists the following approximate retail values as of 04/2010:

No mint mark (Philadelphia):

Very worn condition - $0.06

Moderately worn - $0.08

Slightly worn - $0.14

Almost no wear - $0.60

Uncirculated - $1.20 to $89.70 depending on quality

"D" mint mark (Denver):

Very worn - $0.07

Moderately worn - $0.18

Slightly worn - $0.30

Almost no wear - $1.40

Uncirculated - $2.40 to $80.60

"S" mint mark (San Francisco):

Very worn - $0.07

Moderately worn - $0.19

Slightly worn - $0.36

Almost no wear - $1.20

Uncirculated - $2.64 to $124.80

Answer1940 nickel; With no mint mark, in very fine condition-$0.20, in uncirculated condition-$1.75, proof-$37.50. With D mint mark, in very fine condition-$0.25, in uncirculated condition-$3.75. With S mint mark, in very fine condition-$0.30, in uncirculated condition-$3.75.
If the coin is not uncirculated spend it
$0.40 to $0.50 in average circulated condition
The 1940 Jefferson nickel is very common. Many are still found in circulation today. It's likely only face value unless it's uncirculated.