This is what I do as well. Most of my transactions are done with a credit card, but I do like to use cash ocassionally, especially for smaller purchases below $10...I really do not like to use a credit card to buy something that is $3.79...I don't want too many transactions to track on my statement at the end of the month.
Another thing I do is selectively use cash depending on how much coins I will get as change...for example, if the total purchase is $10.13, I will not use cash because I do not want to get .87 cents change...but if it is $10.92, then I will use cash because I don't mind getting .8 cents change, I just throw it into the cupholder in the center of my car console...by following this practice it takes a lot longer for the change to build up. I also spend it down by using exact change at drive throughs...or I sometimes put some change in my pocket when I go inside a store or a fast food or fast casual restaurant and pay with exact change. By doing these things I generally keep the amount of loose change at a minimum.