Yes, they can both mean the same thing, "to take care of". But be careful of additional meanings of these words... "Tend to" can also mean "has a tendency to"... Ex. - "He tends to enjoy coffee more than tea." Ex. - "He tends to leave work at 5pm instead of 6pm." "Attend" can also mean "visit"... Ex. - "The girl attends a meeting every Wednesday." Ex. - "I want to attend a concert some day."