How many pennies are there in a 5 gallon glass milk jug.  I would like
the answer to be within 5% since I understand that the number will
vary depending on how the pennies are added.  Assume the jug is
completely full.

I am glad the links I posted were useful. I've reposted them below.

"In remembrance of those who lost their lives and out of compassion
for their families and for those who worked hard to help in the
aftermath of 9/11, we at Emerson School decided to celebrate our local
heroes in Plainfield who volunteer as Rescue Squad members.  We called
our effort, ?Pennies to the Rescue?. The children, teachers and
parents collected pennies from September 8 ? 11, 2003.  During our
Harambee meeting on September 11, 2003, each class poured their
pennies into a five gallon water jar. We nearly filled the jar.  It
was spectacular!   Each student had to estimate the number of pennies
collected.  The third grade classes (who were studying Things That
Come in Groups) were in charge of sorting, counting and wrapping the
pennies. They did a tremendous job. A fifth grade student had the
closest estimate of 35,000 pennies. The actual count was 30,294
pennies."

Plainfield Public School District: Math @ Emerson
http://www.plainfieldnjk12.org/Schools/Emerson/Math_at_Emerson/math_at_emerson.html

"...there are exactly 231 cubic inches in a US gallon, this translates
into 231/V, or about 5252.5523 nickels per gallon.  In 5 gallons,
you'd have at most 26262 nickels, worth  $1313.10  (possibly a little
bit more if the walls of the container are shaped to fit the coins,
but much less in a random packing).

For pennies (diameter: 0.75", thickness: 1.55 mm) the above
computation would give a "V" of about 0.029727 cu in, or about 7771
pennies per gallon."

Final Answers: How many pennies, dimes or quarters per gallon?
http://home.att.net/~numericana/answer/trivia.htm#npg

My Google search strategy:

Google Web Search: "5 gallon OR gallons" pennies
://www.google.com/search?hl=en&ie=UTF-8&q=%225+gallon+OR+gallons%22+pennies

Best regards,
pinkfreud

Exactly what I needed.  Thanks for a great (and quick) answer.
Steve

"In remembrance of those who lost their lives and out of compassion
for their families and for those who worked hard to help in the
aftermath of 9/11, we at Emerson School decided to celebrate our local
heroes in Plainfield who volunteer as Rescue Squad members.  We called
our effort, ?Pennies to the Rescue?. The children, teachers and
parents collected pennies from September 8 ? 11, 2003.  During our
Harambee meeting on September 11, 2003, each class poured their
pennies into a five gallon water jar. We nearly filled the jar.  It
was spectacular!   Each student had to estimate the number of pennies
collected.  The third grade classes (who were studying Things That
Come in Groups) were in charge of sorting, counting and wrapping the
pennies. They did a tremendous job. A fifth grade student had the
closest estimate of 35,000 pennies. The actual count was 30,294
pennies."

http://www.plainfieldnjk12.org/Schools/Emerson/Math_at_Emerson/math_at_emerson.html

"...there are exactly 231 cubic inches in a US gallon, this translates
into 231/V, or about 5252.5523 nickels per gallon.  In 5 gallons,
you'd have at most 26262 nickels, worth  $1313.10  (possibly a little
bit more if the walls of the container are shaped to fit the coins,
but much less in a random packing).

For pennies (diameter: 0.75", thickness: 1.55 mm) the above
computation would give a "V" of about 0.029727 cu in, or about 7771
pennies per gallon."

http://home.att.net/~numericana/answer/trivia.htm#npg

Please apply for payment.  That is a great answer.
Thanks