sitniti

1. to chop finely; to mince; to crumble
   Baka sitni luk za paprikaš. — Grandma is finely chopping onions for the stew.
   Svake zime otac sitni drva za peć. — Every winter my father splits firewood for the stove.
2. (of money) to change money into smaller denominations
   Na kiosku često sitnim novac. — I often change money at the kiosk.
   Nemoj da sitniš hiljadarku, imam sitno. — Don't break the thousand-dinar note, I have change.

The perfective counterpart is usitniti; in the sense 'to change money' also rasitniti.