There are 5 grinds to be preformed, all cost 15,000 credits excluding the starting three.
To preform a grind Ollie (press A) and then press the following button commands when there is a something to grind on.
Boardside (Right + Y) - Already purchased
50-50 (Y) - Already purchased
Crooked (Left + Y) - Already purchased
5-0 (Down + Y)
Nose Grind (Top + Y)