Percona xtradb Backup for OLTP I have installed MySQL 5.7 community edition installed.
Can we use Percona xtradb backup tool for backup DB for banking site databases for OLTP?
Percona is a very popular and reputed company. Their products also meet some compliance. So there is nothing to say NO. But you mentioned that this is for Bank. Many banks have their own compliance. So, verify that you are authorized to use 3rd party software. 

But the native mysqldump is not good for taking the large backup set. So its good to use percona's xtra backup or mydumper.