Nicknames for US currency; and why?

You are right about a sawbuck and a fin plus a quarter used to be two bits. However, the only nicknames that I hear now a is a buck for $1 and a grand for $1000

Greenback because the back of paper currency is largely green.

http://4nicknames.com/content/nicknames-money

http://writingexplained.org/slang-for-money

http://forexillustrated.com/currency-nicknames-sec...

Slang terms for money often derive from the appearance and features of banknotes or coins, their values, historical associations or the units of currency concerned. Within a single language community some of the slang terms vary across social, ethnic, economic, and geographic strata, but others have become the dominant way of referring to the currency and are regarded as mainstream, acceptable language (e.g., "buck" for a dollar or similar currency in various nations including Australia, Canada, New Zealand, Sri Lanka, South Africa, Nigeria and the United States).

https://en.wikipedia.org/wiki/Slang_terms_for_mone...

http://www.dailywritingtips.com/50-slang-terms-for...

http://dare.wisc.edu/survey-results/1965-1970/buyi...

http://www.economist.com/blogs/johnson/2010/06/cur...

Coins:

Nickel, for the five-cent coin, because the first replacement for the silver five-cent coin contained nickel, though at only 25% of the weight the rest being copper - the same composition still used today.

Dime, for the ten-cent coin, taken from the French, dime, meaning tithe, or one-tenth part.

Quarter, for the twenty-five cent coin, because it was one fourth of one dollar. Also, 'two bits', from the Spanish dollar or 8 reales coin, or 'eight bits'. It was once common trading practice to cut larger silver coins into pieces. Merchants carried sets of scales around with them to measure the weight, to insure against cheating.

Paper currency:

Sawbuck, for the $10. A sawbuck was a device used for cutting logs, and was rather shaped like an X. The Roman numeral for 10 is X, and it was once used on US $10 notes, so people called these notes 'sawbucks', and $20 notes, 'double sawbucks'.

Fin, for the $5. The word is very similar to the German ( fünf) and Yiddish (finef, finfter) for five. This nickname was once far more common than it is today.

Greenback, for US paper money in general, but mostly the $1. This term came along when green ink was first used to print the reverse sides of notes.

Horse blankets - US notes were once much larger than the size we know today, first introduced in 1929. The term can refer to any large currency, but collectors usually save it for the Series 1923 silver certificates.

Quarter,Dime,greenback,buck