You're misinformed. Rounding is a guideline, not a rule. The rule aspect of it only applies with how much you're allowed to round given the value.

The reason it's usually recommended to round instead, is because should a suggestion like this be off by a key or two for whatever reason (mini is slightly off, a few more keys' worth of value were/were not involved) leads to it having to be resuggested. Rounding eliminates this small factor, meaning that even if the value is off by a few keys, it still rounds therefore it's good enough to be accepted.

There's no issues with this suggestion as it is currently (even if the sale should count as outdated as of this post, this won't be a valid mini should it resell for something), but if there were 1 or 2 more keys added than 250, this would've needed to be resuggested. This is why rounding is a guideline, but it's not a hard rule as you think it is.