If you're talking about the number or quantity of physical objects, it is usual to use the plural:
There aren't any apples.
I don't have any bags for my shopping.
Here, you might have no bags, one bag, or multiple bags; same with the apples.
With mass nouns you wouldn't use the plural, but the meaning is similar.
There isn't any rice.
However, in cases where there is expected to be at most one thing (or only one thing is needed), it is possible to use the singular:
I don't have any key for this door. (Only one key is needed to open a door.)
I don't have any answer for you. (I might have one answer, but not more than one answers.)
There isn't any garden in front of this house. (A house only has one garden, at least in front.)
There isn't any car in the garage. (Assuming the garage is only big enough for one car: if it was a really big garage that could hold multiple cars, then "There aren't any cars in the garage" might make more sense.)
The singular use is perhaps rarer and may sound less natural in some cases, especially where there is uncertainty about whether there is one or more. It is also possible to use an indefinite article: "I don't have a key for this door", etc, but using "any" perhaps provides a bit more emphasis.
You can read a discussion on WordReference about the same thing.