There should be no rounding errors on these settings.
When you changed the Day Setting temporarily did you do it from the round robin or did you use the menu key to get it to the "D" temperature setting to make the adjustment? If you were on the "D" temp screen then you adjusted the setpoint, you did not make a temporary setpoint change.
To make a temporary setpoint change you use the up and down buttons while the control is in the round robin display cycle (where it cycles every couple seconds through current temp, current temp setpoint, and current time). Then when the next programmed setpoint is reached it will assert itself, getting rid of the temporary setpoint.
Neither of these adjustments should affect the night time setpoint, only adjustments while on the "N" programmed setpoint temperature or time screens should do this.
If there is a problem, we definitely want to get you running right. Please call our shop Monday to discuss this issue with us (315-299-3589). We'll likely want to run through a guided programmed setpoint change and a temporary change, and adjust the times for a programmed change in order to make sure they are functioning normally. If we find a problem we'll be more than happy to take it in under warranty.