In spite of Webster 1913, says,
"twopence" is properly pronouced as "tuppence"
(tup"pence'). Although twopence literally means
two pennies, it can also be used figuratively
to refer to any small amount of money.
I wouldn't give you twopence for that cheap toy, squire.
In the Disney movie Mary Poppins, birdfeed costs
twopence a bag. Michael Banks, the young boy that Mary Poppins
looks after, wants to buy a bag from the bird-woman at
St. Paul's Cathedral, but his father won't let him. Instead,
the father wants Michael to put the money in the bank.
Michael refuses and, in the ruckus that follows, causes a run
on the bank. So Michael's father's career at the
bank is (temporarily, at least) ruined; all
for the want of twopence.
Incidently, the beautiful song from the movie, "Feed the birds"
was supposedly Walt Disney's absolute favorite Disney
song.