Google's money proto [1] has units and nanos. Any competent ad-tech system will use something similar: integer number of micro-dollars, nano-dollars, etc. You want a fair amount of precision, so just tracking whole cents isn't enough, but you want that precision to be (linearly) equally distributed across the value space so that you can make intuitive guarantees about how much error can accumulate.
Google's money proto [1] has units and nanos. Any competent ad-tech system will use something similar: integer number of micro-dollars, nano-dollars, etc. You want a fair amount of precision, so just tracking whole cents isn't enough, but you want that precision to be (linearly) equally distributed across the value space so that you can make intuitive guarantees about how much error can accumulate.
[1] https://github.com/googleapis/googleapis/blob/master/google/...