Yes. Custom Portfolios target a small operational cash allocation of 0.5% held at Program Banks that does not earn interest (this is the same as other managed portfolios); when there are fees, withdrawals, or other portfolio management actions, this cash will be used first. The 0.5% cash allocation is required, so when you set your target weights to add up to 100% in the builder, Betterment scales each holding down slightly to make room.
