US retailers reported their best year-on-year monthly sales gains in a decade on Thursday, thanks to Easter holiday purchases and a rise in discretionary spending. Retail Metrics, which tracks monthly retail figures, said its same store sales index rose 8.7 percent in MarchÔÇöthe largest monthly increase since it began tracking the data in 2000. The company said the strong performance was due to the early Easter and easy comparisons with last yearÔÇöwhen the index fell 4.8 percent.