Ulster raced into a 20-5 lead by virtue of their two tries but Munster fought back thanks to a score just before half-time by Ivan Dineen and subsequent efforts from Dave Kilcoyne and James Coughlan.
Indeed Munster worked their way back to 23-19 before two late Pienaar penalties denied them a bonus point and condemned them to only a second RaboDirect PRO12 defeat this season.
Munster did have their chances however, missing their fair share of kicks at goal while in contrast Pienaar was imperious from the tee, and Penney believes that was where the game was won and lost.
"This team have a great deal of fortitude, they were up against an Ulster side who have a great deal of quality," Penney told the Irish Independent.
"We probably left 12 or 15 points out there through our kicking, but it was a great effort. (Ruan) Pienaar kicked everything, that was the difference.
"I'm really disappointed, the lads did a great job. To work our way back to four points down, having not kicked many goals, and giving ourselves an opportunity to score another one was disappointing, but I'm also really pleased with how the guys responded to the pressures."
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