Sometimes this is called checking, were the tiles don't line up evenly. There is no way to solve this problem, but you can fill the cracks by applying an acrylic polish. A good acrylic polish is Armstrong Shine Keeper. The last thing you want to do is go around the floor putting caulk in the cracks, and especially don't use silicone caulk. Silicone caulk is not a water clean up product, and would cause a huge mess.