Constructing and Designing Class Diagrams

I have the following scenario where I have to design a class diagram :

A grocery store (e.g., a supermarket) sells items. There are two types of items: edible (i.e., any item that can be used as food) and non-edible. Some items are sold by weight, and some are sold per unit. Some items are taxable, while others are not. Some items have special prices when sold in groups (e.g., 2 for $3). A purchase may contain many items.

The points need to be considered are :

• An item is either edible or not and this fact does not change during the lifetime of the item, whereas the pricing strategies may change during the lifetime of the item.
• Each pricing strategy is associated with a certain set of operations. For example, for the taxing strategy, whether or not an item is taxable, we may have an operation that computes the tax (this function can then return 0 for non-taxable items)
• Although the set of operations for a pricing strategy stays the same, the ways those operations are handled may change over time. For example, the way we compute taxes for edible and non-edible items may differ over time.
• Although the set of operations for a pricing strategy stays the same across different items, we may want to implement those operations in different ways for different items. For example, we may want to compute the tax differently for oranges and apples.

I know it must be a strategy design pattern. I am thinking of doing a PricingStrategy interface and implement the strategies but I am not sure of them. Moreover, I may create an Item super class and Edible and Non-Edible Items can inherit the class however nothing is clear in my head, any help is appreciated.