If you are collecting for the long run, it is a good habit to keep your Tomicas in plastic covers and they come in three sizes listed below. They don't cost much and are usually sold in bundles of ten pieces. If your toy store is kind enough or professional in business, the cars you get would have already been encased with them.
They proved quite useful to keep out dust and more importantly protect the items. Do note that while the plastic cover itself may suffer from discolouration over time, I was assured by another collector that the original car box is not affected 💚
Sizes of Plastic Covers
Regular Box (small) and Regular Box (large)
Tomica Limited Box (largest)