If it is paid out evenly and as wages it will be about 66k SEK/month per employee, that puts them well into the top tax bracket. Assuming the tax authority counts it as normal income they will be force to pat ~56% income tax a fair bit of social securities and employer tax. Assuming this they might get about (as a guesstimate) 20-25k SEK/m or 240-300k SEK total, after taxes. Not shabby at all, that is close to what an average worker in Sweden earns per year. And that is bonus alone.
None the less; Cheers Notch for thinking about your employees! : )
Edit: Gifts are no longer taxed in Sweden, luckily! but it is likely that the tax authority will regard it as income or bonus rather than a gift.