Two retail industry groups — discounters and department stores — bucked the market's weakness Tuesday. Dollar Tree (DLTR) led the move by discount retailers. The 3,600-store chain gapped up to a 5% gain in heavy trade after reporting its Q3 earnings soared 61%. That topped analysts' consensus estimate by more than 15%. The company also boosted its full-year earnings and sales guidance. Sales of health and beauty products and cleaning supplies were