```python
from typing import *
from collections import *

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 < 0 or rate > 100:
        raise ValueError("Rate must be between 0 and 100")
    
    tax = (rate / 100) * net
    rounded_tax = math.floor(tax)
    return net + rounded_tax
```