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 $104.49   12.242%   $117.2817   $117.28   $117.30   $117.30  
  Purchase #2 $164.46   10.686%   $182.0342   $182.03   $182.05   $182.00  
  Purchase #3 $39.90   10.411%   $44.054   $44.05   $44.05   $44.10  
  Purchase #4 $67.70   13.598%   $76.9058   $76.91   $76.90   $76.90  
  Purchase #5 $218.96   13.307%   $248.097   $248.10   $248.10   $248.10  
  Purchase #6 $179.59   7.724%   $193.4615   $193.46   $193.45   $193.50  
  Purchase #7 $57.44   9.449%   $62.8675   $62.87   $62.85   $62.90  
  7 purchase totals = $832.54       $924.7017   $924.70   $924.70   $924.80