The specificity comes not on a case-by-case basis, but from the agreement reached by the league and the NFLPA regarding the minimum amounts for various infractions.
For physical contact with an official, for example, the minimum player fine is $26,250 on a first offense. Verbal or non-physical offenses against officials entail a less specific $21,000 fine for a first offense.
For striking, kicking, or kneeing an opponent, the minimum for a first offense is $7,875.
Horse collar, first offense? $15,750 minimum.
Face mask, late hit, low block, chop block, taunting? $7,875 minimum.
Leg whip, roughing the passer? $15,750 minimum.
Spearing, hit on defenseless player, blindside block, impermissible helmet use? $21,000 minimum.
Fighting? $26,250 minimum.
Excessive profanity or other unsportsmanlike conduct triggers a minimum fine of $10,500.
Foreign substances on the uniform/body or failure to wear a chin strap results in a minimum fine of $7,875.
Throwing a football into the stands or personal messages on the uniform draw a minimum fine of $5,250.
For second offenses, all minimum fines double.