This is perfectly fine! Our society is so hung up on boys being boys and girls being girls, and oh my gosh, if they dare steer to the other side, they are going to be gay! It's not true! We are so stereotypical in our society. We think girls should play with dolls, learn to cook with toy kitchens, play dress up, etc. We think boys should play with trucks, should play in the mud, should play soldiers, etc. In our society, women are doing a man's job...and men are doing a woman's job.
A child psychologist told me once that when a boy gravitates towards girls and towards playing with dolls, it's because he has a very nurturing side to him. It's part of his personality. If a girl gravitates towards boys or towards rough and tough playing, it's because she's adventurous and wants to be carefree.
I was a tomboy as a little girl. I did not like playing dress up. I played with boys. I hated dresses. I loved Ninja Turtles. Yes, I had some dolls, and I'd play with them on occasions. I loved remote control cars, skateboards, and "boy toys". I grew up to have mostly guy friends and still am that way! I am now 29 yrs. old, a mom to a little girl who is the SAME way I was (except she loves dresses and loves to play in makeup), and I'm married.
I have a nephew ("D.") who was the exact same way your son was. He wanted to play with dolls. He's 11 yrs. old now and is the sweetest, most caring, and most nurturing little boy you'd ever meet. I have a 9 yrs. old sister, who is 2 yrs. younger than her own nephews (they are twins). My little sister loves playing with "D". He'll play Barbies, dolls, house, etc. with her. My sister was always told by others to not let her son play with dolls, but my mom always told my sister that it just teaches him to be nurturing and loving, so my sister would let him do it at my mom's house. Because my sister never made a big deal of it, my nephew has never seen anything wrong with it. No one in the family teases him. He's a regular 11 yr. old little boy. He also loves to do what other little boys his age like to do (video games, bikes, 4 wheelers, fishing, etc.). Letting boys play with dolls actually helps them to grow up to be nurturing, loving, and caring. It teaches them parenting skills. It teaches them to respect women.
Just let your little boy play with what he wants. It's no big deal! You'll find that your son will grow up with a great admiration of you because you always let him "be himself".