YOU SAID:

I went to a store to buy a box of cereal.

INTO JAPANESE

私はシリアルの箱を買いに店に行きました。

BACK INTO ENGLISH

I went to the store to buy a box of cereal.

INTO JAPANESE

私はその店にシリアルの箱を買いに行きました。

BACK INTO ENGLISH

I went to the store to buy a box of cereal.