Objective: Effective canal debridement and shaping are fundamental to endodontic success. The use of nickel–titanium (NiTi) rotary instruments has significantly improved the predictability and quality of root canal preparation, especially in curved canals. This study aimed to assess and compare canal taper and regularity achieved using five different NiTi rotary systems. Material and Methods: One hundred extracted human mandibular molars with three distinct canals were randomly allocated to five groups (n = 20), each instrumented using one of the following NiTi rotary systems: BioRace, ProTaper Universal, Mtwo, HEROShaper, and K3. Root canal impressions were made and evaluated under a stereomicroscope at 10× magnification. Each canal third (cervical, middle, and apical) was evaluated separately. The following criteria were used to classify canal shaping: RCTR – Regular canal with a conical shape; ICTR – Irregular canal with a conical shape; RCTS – Regular canal with a cylindrical shape; ICTS – Irregular canal with a cylindrical shape. Statistical analysis was performed using the Fisher’s exact test (p < 0.05). Results: The RCTR category was predominant across all groups. BioRace and K3 systems demonstrated consistent performance among the root thirds, whereas ProTaper exhibited significant variation, with a higher frequency of RCTS in the cervical third and RCTR in the apical third (p < 0.05). Mtwo and HEROShaper showed intermediate outcomes without statistically significant differences across thirds. Conclusions: Although differences were more pronounced in the middle and apical thirds, the predominance of the RCTR pattern across groups indicates satisfactory shaping ability for all systems.