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Routing load balancing generally directs packet flows to the same path. This to maintain flow packet sequence.
Path selection, per flow, might be round robined, i.e. "cycles" to the next path when there's a new flow. Or it might be deterministic based on flow's attributes (similar to Etherchannel). (I recall CEF might be deterministic, as I also recall there's a way to change CEF bias for optimal load balancing across multiple hops.)
Some routing will round robin individual packets, as does optional CEF packet-by-packet (as noted by the other posters), and process switched packets are round robined too, I believe.
Most routing load balancing is only for supported for equal cost paths but Cisco's EIGRP supports unequal cost paths (proportional sharing).
Most routing load balancing doesn't account for current interface load but Cisco's OER/PfR can perform dynamic load balancing, i.e. it can track actual interface usage. It can move individual flows to specific egress interfaces. (It also supports proportional loading.)
