Description
Pandas version checks
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I have checked that this issue has not already been reported.
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I have confirmed this bug exists on the latest version of pandas.
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I have confirmed this bug exists on the main branch of pandas.
Reproducible Example
import pandas as pd
dates = pd.Series([pd.to_datetime("2022-01-11 12:10:00")])
# date should be rounded but is not
dates.round("30min")
# >0 2022-01-11 12:10:00
# >dtype: datetime64[ns]
# Round just date works
dates[0].round("30min")
# >Timestamp('2022-01-11 12:00:00')
Issue Description
Issue with the latest version of pandas (2.2.0). Rounding dates at 30 min increments does not round dates if they are in a series. This was working in pandas (2.1.4)

Expected Behavior
Dates should be rounded to 30 minute increments
import pandas as pd
dates = pd.Series([pd.to_datetime("2022-01-11 12:10:00")])
# Round just date works
dates[0].round("30min")
Installed Versions
INSTALLED VERSIONS
commit : 53525ea
python : 3.10.0.final.0
python-bits : 64
OS : Linux
OS-release : 5.15.133.1-microsoft-standard-WSL2
Version : #1 SMP Thu Oct 5 21:02:42 UTC 2023
machine : x86_64
processor :
byteorder : little
LC_ALL : None
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8
pandas : 3.0.0.dev0+152.g53525ea1c3
numpy : 1.26.2
pytz : 2023.3.post1
dateutil : 2.8.2
setuptools : 68.2.2
pip : 23.3.1
Cython : None
pytest : 7.4.3
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : 3.1.9
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 3.1.2
IPython : 8.18.1
pandas_datareader : None
adbc-driver-postgresql: None
adbc-driver-sqlite : None
bs4 : 4.12.2
bottleneck : None
dataframe-api-compat : None
fastparquet : None
fsspec : 2023.12.2
gcsfs : 2023.12.2post1
matplotlib : 3.8.2
numba : 0.58.1
numexpr : None
odfpy : None
openpyxl : 3.1.2
pandas_gbq : None
pyarrow : 14.0.1
pyreadstat : None
python-calamine : None
pyxlsb : None
s3fs : None
scipy : 1.11.4
sqlalchemy : None
tables : None
tabulate : None
xarray : None
xlrd : None
zstandard : None
tzdata : 2023.3
qtpy : None
pyqt5 : None