Krishna Panchami is the name for the 20th Tithi (lunar day). It's the 5th Tithi of Krishnapaksha. It's nature is Lakshami Prada, which can be interpreted as "wealth giver" (as through this Prada Panchami is connected to Lakshmi Devi, who rules all wealth matters in human life). It's good for following works: all auspicious works; Upanayana, Paushtik works, Manglik Utasav; house matters (Griha Shanti); travel, stationary and moving actions. Money lending is prohibited and should be avoided.
According to Muhurta Chintamani the Nāga (Deity who rules Serpents) rules Krishna Panchami, thus it is favorable for all actions that are related to what Nāgas are responsible for: gaining wisdom, secret knowledge. Nāgas also are related rebirth, administering medicine, the purging of poisons, and surgery, as well as waters (rivers, lakes, seas, and wells) and are generally regarded as guardians of treasure. According to Brihat Samhita Panchami is ruled by Chandrma and all actions done in respect of Chandrma (mother, Apas, emotions, etc) are acceptable during this day.
Being Poorna (that can be translated as full", "complete" or "perfect") and ruled by Guru (Jupiter), the 5th Tithi of Krishnapaksha is suitable for following works or actions: marriage, Upanayana, Manglik works, travel, tourism, coronation, peaceful & Paushtika actions.
During the vedic months Kartika and Pausha Krishna Panchami becomes Maasa Shoonya Tithi, which is considered inauspicious in succeeding in works started during this Tithi.
Lagna (ascendant or rising sign) during Krishna Panchami becomes Tithi Shoonya (Lagna which is ruined by Tithi) for times when it is Mithuna (Gemini) or Kanya (Virgo). Magha Nakshatra also become Tithi Shoonya if it falls on Krishna Panchami. It's considered that all auspicious works done during Tithi Shoonya periods will be destroyed.