What is one of the first things your Mother taught you.....to take care of your toys! Well in this instance, it is your gardening tools.
Proper maintenance will increase the longevity of your tools and prevent any soil contamination.
My recommendation is simple.......a bucket of sand and some linseed oil.
You can get "fancy" with your container and use a terra cotta pot or something similiar like pictured, or just use a plain old bucket.
You will need a bag of sand linseed oil.
There are articles about using old motor oil but I would frown on that because you are adding a contaminate to your soil. Linseed oil will prevent rust on your metal blades and can also be used to condition the wood handles.
Go to Home Depot and pick up a can of linseed oil and a bag of sand.
Make sure there is a drainage hole in the bottom of your container, Empty the sand into your container and pour the linseed oil in. Not the entire container at one time, let it set a bit and mix it up with your trowel. It should be damp with the oil but the oil should not be pooling.
When you are done you can store your hand tools in here as well as clean your long handled tools in here as well.