Teens have known for a long time that five-and-dime stores are a great place to shop, especially for summer clothes, accessories and makeup. For less than the price of a pair of designer jeans, you can fill a shopping cart with everything from tank tops to bathing suits. With a little more searching, you can find inexpensive versions of up-to-the-minute fashions. And even if inflation has made them five-and-ten dollarstores, they are still a welcome relief in these expensive times. So save money--and use it to go to the beach. CAPTION: Picture 1, purple polished-cotton shorts ($6.99) and white tank top with abstract print by Island Fun (two for $7), both at S.S. Kresge; yellow bangle with abstract design ($2.99) at Woolworth's; collapsible aviator sunglasses ($4.88) at Ambassador Drugs. Picture 2, multicolor, horizontal-stripe maillot by Windmills ($14.99) and magenta quartz digital watch by Nelsonic ($3.97), both at G.C. Murphy; red rubber shoes ($7.99) at Ben Franklin. Picture 3, turquoise rubber shoes ($7.99) at G.C. Murphy; multicolor squiggle bangles (three for $1.98) at Ambassador Drugs. Picture 4, red tinted straw visor ($1.79) at S.S. Kresge, round earring ($1) at Ben Franklin.