Any transaction of < 0.01 BTC attracts a transaction fee, which most clients default to 0.0005 BTC. At present 'market' rates ( $179 per BTC as I type ), that

Any transaction of < 0.01 BTC attracts a transaction fee, which most clients default to 0.0005 BTC. At present 'market' rates ( $179 per BTC as I type ), that means that the tipper has to give $1.79 to avoid incurring a fee, and the recipient should wait until their stash exceeds that level before transferring to their wallet. Which is good practice, anyway, to avoid creating lots of wallets with small values that can't be ( affordably ) used.