Better if you have a tape deck equipped with "Line out" - if using headphone out, be sure to turn off anything that may alter the sound.
If they are commercial tapes using Dolby:
1. You are technically violating copyright, unless in a part of the world where "fair use" concepts are sensibly applied
2. Use Dolby compatible equipment, so that Dolby noise reduction is applied.
Dolby boosts the high frequencies in passages where they are low, so a Dolby recording played on non-dolby equipment may sound a little bright.