```python
def gross_price(net: int, rate: int) -> int:
    """A net price with a whole-percent tax added, in whole pence."""
    if rate == 0:
        return net
    elif rate > 100 or rate < 0:
        raise ValueError("Rate must be between 0 and 100")
    else:
        tax = round(net * (rate / 100), 0)
        return net + tax
```