too much space with tabto and enumitem

Question

The MWE below indicates the problem. The final item, number 6, isn't aligned correctly (it is pushed some extra space to the right!). This is also the case when I change the number of tabs to 2.

\documentclass{article}
\usepackage[inline,shortlabels]{enumitem} 
\usepackage{tabto}

\begin{document}

\NumTabs{3}
\begin{description*}[before={\noindent},itemjoin={\tab}]
\item {1.} 
\item {2.} 
\item {3.} 
\item {4.} 
\item {5.} 
\item {6.} 
\end{description*}

\end{document}

Answer 1

Insert after={\hfill} in the description* options.

MWE

\documentclass{article}
\usepackage[inline,shortlabels]{enumitem}
\usepackage{tabto}

\begin{document}

\NumTabs{3}
\begin{description*}[before={\noindent},itemjoin={\tab},after={\hfill}]
\item {1.}
\item {2.}
\item {3.}
\item {4.}
\item {5.}
\item {6.}
\end{description*}

\end{document}

Output:

---

EDIT

To be able to do what you ask in the comment, we need to issue \hfill\par before the closing brace, otherwise the paragraph is not ended. For explanations see, for example, Incorrect line spacing when using \Large in a center environment.

This can be done with the help of the etoolbox package and the line

\AfterEndEnvironment{description*}{\hfill\par}

that adds \hfill\par after description* has ended.

MWE:

\documentclass{article}
\usepackage[inline,shortlabels]{enumitem}
\usepackage{tabto}
\usepackage{etoolbox}
\AfterEndEnvironment{description*}{\hfill\par}

\begin{document}

{\tiny\NumTabs{3}
\begin{description*}[before={\noindent},itemjoin={\tab},after={\hfill}]
\item {1.}
\item {2.}
\item {3.}
\item {4.}
\item {5.}
\item {6.}
\end{description*}}
\bigskip

\NumTabs{3}
\begin{description*}[before={\noindent},itemjoin={\tab},after={\hfill}]
\item {1.}
\item {2.}
\item {3.}
\item {4.}
\item {5.}
\item {6.}
\end{description*}
\bigskip

{\Huge\NumTabs{3}
\begin{description*}[before={\noindent},itemjoin={\tab},after={\hfill}]
\item {1.}
\item {2.}
\item {3.}
\item {4.}
\item {5.}
\item {6.}
\end{description*}}

\end{document} 

Output:

Answer 2

An alternative to an enumerated list in two or three columns is the multienum package:

\documentclass{article}
\usepackage{multienum}
\begin{document}

\begin{multienumerate}
\mitemxxx{One}{Two}{Three}
\mitemxxx{Four}{Five}{Six}
\end{multienumerate}

\end{document}