OK... It turns out I was wrong. On the receipt they don't round to the nearest dollar. I had $17.75 in rewards after my last visit, but when I went yesterday my receipt said I had $17 in rewards. I spent $71.84 before tax, including a $25 GC for $23.99 and today I had $18.71 in rewards, which is exactly what it would be if I didn't get the rewards for the GC.