Try this. Make sure Snap is on and move the Audio so the start snaps to the grid. On the Arrow Tool choose the option “Sizing Applies Time Stretch.” Now drag the end of your audio so it stretches (or shrinks) and snaps to a bar line. Now the timing between the audio and Cubase should be aligned. If you need to delay (plus or minus) the audio clip a bit there is a control in the Inspector for that.
Then in the Pool click the checkbox next to your audio to set it to be in Musical Mode. This tells that specific audio to follow tempo changes. On the Track with the audio on it, set the Track to Musical Timebase this tells the Track to position items on the timeline based on Bars & Beats. If set to Linear Timebase then items on the Track would be positioned based on hh:mm:ss (not what you want, but film folk need this).