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 $126.29   6.826%   $134.9106   $134.91   $134.90   $134.90  
  Purchase #2 $108.77   5.688%   $114.9568   $114.96   $114.95   $115.00  
  Purchase #3 $182.44   10.167%   $200.9887   $200.99   $201.00   $201.00  
  Purchase #4 $68.86   11.177%   $76.5565   $76.56   $76.55   $76.60  
  Purchase #5 $101.85   12.311%   $114.3888   $114.39   $114.40   $114.40  
  Purchase #6 $121.83   13.806%   $138.6498   $138.65   $138.65   $138.60  
  Purchase #7 $83.46   10.518%   $92.2383   $92.24   $92.25   $92.20  
  7 purchase totals = $793.50       $872.6895   $872.70   $872.70   $872.70