Were federal offices closed for the funerals of Nixon and Johnson or
just for Reagan?

With the exception of emergency operations, all federal offices were
closed in a national day of mourning after the deaths of LBJ and
Richard Nixon. January 25, 1973 was the official day of mourning for
Johnson, and April 27, 1994 was the official day of mourning for
Nixon.

"The special day of mourning for President Reagan jogged the memories
of many feds who wanted to know about how the deaths of other
presidents were observed. Some wanted to know, or verify, what the
policy was when Presidents Nixon and Johnson died...

Non-emergency (they were called 'non-essential' in those days) federal
workers got a day of mourning on the day of President Johnson's state
funeral. They got a day of mourning off on the day President Nixon was
buried."

Federal News Radio: Day Of Mourning Recollections and Rules
http://www.federalnewsradio.com/index.php?nid=22&sid=111248

"The practice of allowing federal employees to participate in a
national day of mourning began on Nov. 25, 1963, three days after the
assassination of President John F. Kennedy, said Mike Orenstein,
spokesman for the federal personnel office.

The day of mourning was repeated after the deaths of four other former
presidents - Dwight D. Eisenhower in 1969, Harry S. Truman in 1972,
Lyndon B. Johnson in 1973 and Richard Nixon in 1994."

WPIX-TV: Funeral May Be Pricey for U.S. 
http://wb11.trb.com/news/local/ktla-na-cost10jun10-lat,0,6343223.story

"On Nixon's death in 1994, President Clinton declared an official day
of mourning and closed the federal government for a day, as had been
done upon the deaths of former Presidents Truman, Eisenhower, and
Johnson."

Anecdotage: Federal Holiday
http://www.anecdotage.com/index.php?aid=13568

Google search strategy:

Google Web Search: "federal offices" + "closed" + "nixon" + "johnson"
://www.google.com/search?hl=en&ie=UTF-8&q=%22federal+offices%22+closed+nixon+johnson

I hope this information is helpful. If anything is unclear, please
request clarification; I'll be glad to offer further assistance before
you rate my answer.

Best regards,
pinkfreud

Great answer ... seems a costly gesture for the taxpayers, however ..
perhaps just an hour or two to attend a memorial would be better

I just came across this interesting statistic:

"One day's federal payroll is about $423 million."

http://www.mercurynews.com/mld/mercurynews/news/opinion/8889994.htm?1c