One of the owners of the company I work for ...
I would honestly recommend a thank you card (ie, a "Hallmark" type card).
Any sort of gift is somewhat strange.
No matter how nice the person is, you're an employee and they're an owner.
Which means:
Say you worked there 10 years and were paid for example $1m in total. Through your work, the owner would have made tens of millions of dollars.
Once you realize that, the idea of gifting an owner, is both fatuous and bizarre, and indeed extremely misguided.
Keep things business-like.
To repeat:
No matter how nice the person is, you're an employee and they're an owner.
To repeat:
The owner would have made vastly more from your work than you were paid for your work.
Footnote about owners "retiring" ...
When an owner "retires" from a business, that means the business has "worked out" for the owner - to wit, the owner now continuously, forever, gets money weekly from the business and does nothing. IE the owner no longer needs to show up every day and now does nothing, continuously forever getting (a lot) of money due to the ongoing work of the employees.
Realizing this, you can see it's doubly-bizarre that an employee would give gifts to an owner.