Petty sums refer to a small or insignificant amount of money, and there are a number of synonyms that can be used to describe such sums. For instance, some alternatives might include trivial amounts, negligible funds, inconsequential sums, or paltry cash.
Other possibilities could include minor finances, meager monetary amounts, small potatoes, or piddling sums. Regardless of the term that is used, however, it is important to remember that petty sums can still add up over time and impact a person's financial situation in significant ways. As such, it is important to be mindful of even seemingly small expenses and to manage them wisely.