Do the amounts received correlate to the mixin level when sent?
When sending a payment, the amounts are split by denominations, such that every single output's decimal representation is made up of a single non zero digit, and zeroes for the remainder.
For instance, 875.4 would be split into 800, 70, 5, and 0.4. If you're sending, or receiving, 875.4, the protocol will be sending these 4 different outputs. The intent is to make it easier to find other outputs of the same amount on the blockchain, so they can be mixed (this will become moot when RingCT transactions are used).
Mixin has essentially no relevance for this (on the output splitting side).
No. It just splits the transaction amout into denominations commonly found on the blockchain. Then, each of those denomitation is mixed with few more of the same kind, depending on the mixin level specified.
This is to ensure there are always plenty of denominations avaliable to mix with. If you used arbitrary amouts like a single 0.324123 transaction, it would be very unlikely to find another one of the same amount. This problem is solved by always splitting the amounts, automatically, to denominations.