Database
[{"_id":1,"name":"xiaoming","time":400,"mon":100.7645234},{"_id":2,"name":"xiaoming","time":400,"mon":200.7645234}]
Query
db.collection.aggregate([{"$group":{"_id":"$name","count":{"$sum":{"$divide":[{"$trunc":{"$add":[{"$multiply":["$mon",100]},0.5]}},100]}}}},{"$set":{"name":"$_id"}},{"$project":{"_id":0}}])