Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $223.67   11.192%   $248.7031   $248.70   $248.70   $248.70  
  Purchase #2 $225.81   4.381%   $235.7027   $235.70   $235.70   $235.70  
  Purchase #3 $52.87   6.867%   $56.5006   $56.50   $56.50   $56.50  
  Purchase #4 $208.59   11.739%   $233.0764   $233.08   $233.10   $233.10  
  Purchase #5 $136.89   8.696%   $148.794   $148.79   $148.80   $148.80  
  Purchase #6 $169.55   8.540%   $184.0296   $184.03   $184.05   $184.00  
  Purchase #7 $182.34   8.627%   $198.0705   $198.07   $198.05   $198.10  
  7 purchase totals = $1,199.72       $1,304.8769   $1,304.87   $1,304.90   $1,304.90