You are conducting external audit on behalf of your firm, on the last day of audit, you received gift from your company. So can we accept the gifts ?

Gifts fall into3 categories:

1) Trivial.  This is a simple social gesture.  Trivial gifts have little or no value of any kind. Examples might be a thank you card or giving somebody a lift to the railway station.  This technically has the monetary value of the cab fare, but a) that's so small in the context of a business trip it's functionally zero and b) that's not the purpose of the gift, which is a social thing

2) Declarable.  This is a gift which does have a small value.  Many organisations specify a limit.  For example, patients sometimes give healthcare professionals a gift at the end of their treatment: this is a perfectly acceptable practice as long as the gift is not worth too much and is declared to the employer.  

3) Unacceptable.   This is a gift which has some real value and could be construed as a bribe.  Such gifts are either politely declined, or must be passed on to a third party in a manner which could not be construed as a bribe (e.g. to a charity totally unconnected to the gift receiver).   Such un-received gifts must also be declared to the employer. 

To give an idea of the level, in the health service in the UK gifts over £ must be declared and over £ are not permitted.   ('Minimum wage' is £7. per hour.)   Appropriate levels may vary depending on cultural norms.

If you believe that a "gift" actually is a bribe, you should inform the police.

In the case of an auditor, the rules must be enforced by the auditors themselves with extra strictness.  If you are not% comfortable with telling everybody, including the shareholders, about it then you must not accept it.  

Note that some industries and companies have tighter rules.  And that some others, and indeed some countries, have a somewhat different attitude to "gifts".