I have had exactly the same discussions with my walking group members, (60 at the moment), regarding which miles to count and which not. One member says she counts all the walking she does, including shopping. Another said she was doing it all wrong then because she only counts the times that she actually goes for a walk. I went through the whole rigmarole of explaining what you have been talking about here, there are no rules, it isn't a competition, it isn't a race, and it's silly to compare yourself with others.
Personally I check mine with bikehike, I only count the miles when I am actually going out for a walk. I don't count dog walking because the dog keeps stopping and I want to walk fast. I don't count bimbling, meandering, strolling, and pottering around town. I don't count parts of a mile, I round up when it's more than half a mile, and round down when it's less than half a mile. I don't care what anybody else is doing.
ilona