1934 penny with mint mark

Normally the question has to be asked "WHICH mint mark?". However the only 1934 cents with a mint mark came from Denver so your coin has a D below the date.

Most circulated 1934-D cents are only worth a small premium - 15¢ or so in worn condition up to a half-dollar with only moderate wear.

However nice 1934-D cents in almost-uncirculated or uncirculated condition are scarcer and can be worth $5 to $10 depending on how well-struck they are.