Yani kani cha papani 
Janmantara kritanicha 
Tani tani vinashyanti 
Pradakshinam pade pade 

yani kani--whatever; ca--and; papani--sins; Janmantara - this birth and earlier births; kritani - done (by me); ca--also, tani tani--all of them; vinashyanti -- are destroyed; pradaksinam-- (by) the self circumambulation ; pade pade--at every step. 

I (self) rotate in my place to kill all my sins that I may have committed in all of my my births! 

2) What times this mantra can be chanted? 

Pradakshina around ourselves is done at the end of all poojas at our houses. 

3) What is the purpose chanting this way? 

The God which we have seen outwards is also inside! 

Katha Upanishad, 2.1.12: 

2-I-12.The Purusha, of the size of a thumb, dwells in the body. (Realizing Him as) the Lord of the past and the future, one does not (henceforward) want to protect oneself. This verily is that (thou seekest). 

Svetasvatara Upanishad, 5.8: 

V-8: Subtle as the point of a goad, and pure, effulgent and infinite like the sun, He alone is seen assuming as another the size of a thumb on account of the finiteness of the heart (in which He appears), and associating Himself with egoism and Sankalpa on account of the limitations of the intellect. 

4) What is the tatwartha here? 

The Omnipresence God is not only everywhere and inside ME but ALSO in each one of all living and non living things!! Do not harm any !!! 

Katha Upanishad, 2.3.17: 

2-III-17. Purusha of the size of a thumb, the inner Self, is ever seated in the heart of all living beings. One should, with steadiness, separate Him from one’s own body as stalk from the Munja grass. One should know Him as pure and immortal; one should know Him as pure and immortal. 

Svetasvatara Upanishad, 3.13: 

III-13: Assuming a form of the size of a thumb, by virtue of intellect, emotion, imagination and will, the Infinite Being dwells in the hearts of creatures as their inner self. Those who realize this become immortal. 

5) Marathi Bhajan, "Dhanya Dhanya Ho Pradakshina" : 

MP3 audio from: 

http://www.mazafm.com/marathimusic/detai... 

धन्य धन्य हो प्रदक्षिणा सद्ग़ुरुरायाची/ 
झाली त्वरा सुरवरां विमान उतरायाची// ध्रु. // 

I am very happy to do pradakshina around Him. He is inside and I go around. I surrender to Him. I am winding myself around the Master so that I may always be with Him. 
At once Gods have sent an air-vehicle down to take me up and I have become HE. Gods themselves are in haste to come down and I have done pradakshina to such a great One because the unmanifest has become manifest. 

पदोपदी अपार झाल्या पुण्याच्या राशी/ 
सर्वही तीर्थे घडली आम्हां आदिकरुनि काशी/ धन्य.//१// 

By doing pradakshina, pilgrimages, the main pilgrimage is to Kashi (body) where Master gives you understanding and you become HE. There is a mountain of virtue on my behalf. 

मृदंग टाळ घोळ भक्त भावार्थे गाती/ 
नामसंकीर्तने ब्रम्हानंदे नाचती/ धन्य. //२// 

Different drums and cymbals are played by disciples with love as we chant HIS name. 

कोटि ब्रम्हहत्या हरती करितां दंडवत्/ 
लोटांगण घालिता मोक्ष लोळे पायात/ धन्य. //३// 

By your grace, the Master key to removing the sin of „killing a Brahmajanani", (Reality Is dropped and you say I am a body) is surrendering to the Master. 

गुरुभजनाचा महिमा न कळे आगमानिगमांसि/ 
अनुभव जे जाणती ते गुरुपदिचे अभिलाषी/ धन्य. //४// 

The secret of the Master‘s Praise (Guru Bhajan) cannot be understood by scriptures or ritual. Only those who have greed for always being at the Master‘s feet,(knowledge:I am HE) will understand. He takes you beyond knowledge. 

प्रदक्षिणा करूनि देह भावे वाहिला/ 
श्रीरंगात्मज विठ्ठल पुढे उभा राहिला/ धन्य. //५// 

By making pradakshina and by my dedication, (I am not the body, I am HE), I become the real prosperity, the SELF, one with Vitthala.(Reality)