Note: Low decimal tokens are in scope as per the README.
In CreatorRoyaltiesControl.sol contract (which is inherited by PhiNFT1155.sol contract), rounding down of royalties is possible if salePrice is denominated in a token that has low decimals. 
For example, royaltybps = 10 (i.e. 0.1%) and salePrice = up to 999 (meaning up to 0.999 tokens for a token with two decimals). When we perform calculations, the royaltyAmount would be returned as 10 * 999 (max) / 10000 = 9990/10000 = 0. 
According to EIP 2981:
This is optional to the protocol as mentioned by the spec but since it could result in the royalties not being received by the artist, it is a valid issue to consider.
Note we can also see the IERC2981 inherited contract in CreatorRoyaltiesControl.sol which mentions: 
This further proves that the contract is supposed to support and return royalties in any unit of exchange requested by an external marketplace, which isnt currently done. 
