Stealing

Salaam Mufti Sahib. During my youth I worked for a good muslim man & due to my greed I stole some money from him. I am now self employed and Alhamdulillah Allah has shown me the staright path and I am trying to sort out my life. I am unfortunately not able to recall the exact amount I took from my boss, so how do I go about calculating the amount as I have a only a vague idea of the amount taken. Also, since I still meet him regularly & he still holds me in high esteem, how do I repay him & ask for forgiveness without him knowing it is me that did this?