In the old days, it was believed that you would save gas by leaving your car running if you planned to use it again within a few minutes. That has probably become less true over time as cars have gotten more and more efficient over time. Apparently, idling your car for even something like 10 seconds uses more gas than turning it off and on again. This is caused by the use of fancy fuel systems that cars use now. This technology is, of course, leveraged in hybrids which turn their internal combustion engines off and on as needed.
Anyway, here is an infographic that provides the details. The simple answer is, no, idling the vehicle is generally not a good idea, so stop doing that.