If it’s a past habit : use imparfait.

À l’époque, j’allais au magasin tous les jours.

“A l’époque” seems to span over a long time, and hence express a habit. Passé composé would be a meaningful candidate too if you were not starting with “à l’époque”. If it were not a habit, but just a series of occurences over a short interval of time, like in “I fell in love with that sales assistant, and I went to the shop every day for a week”, you could have said :

Cette semaine là, je suis allé au magasin tous les jours.

However, you’ll be perfectly understood whichever you choose, none being felt as a mistake. The difference is meaningful if you’re really looking to express a detailed connotation about going to the shop being a habit or not.

Conditional is inappropriate, unless you’re talking about a past wish that never came true, in which case futur antérieur would be a more literate choice anyway.

The imparfait is the correct choice.

As a rule of thumb, imparfait can be used to speak of events that spanned a substantial period of time in the past, while passé composé can be used to refer to specific events in the past.

Eg:
Imparfait: “Je jouais au football quand j’habitais à Paris”

Passé composé: “J’ai joué au football avant-hier”