To do this, set your sequence to play at the loudest section of the song. Record this section onto the cassette. After you record the section, play back the cassette. If you don't hear any distortion, re-record the section at a slightly higher level. Don't worry about the record indicators on the cassette deck.
Some tapes can record at very high levels without distorting the sound.
If you hear distortion on playback, lower the record level and try again. Once you have set the level for the loudest part of the sequence, you won't have to worry about the rest of the song. Cassette tapes do not have the dynamic range of CD recordings. A few loud snare drum hits or bass drum hits can force you to lower the recording level for the entire song. Watch your record meters while your sequence is playing.