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 $167.36   5.611%   $176.7506   $176.75   $176.75   $176.80  
  Purchase #2 $246.60   6.197%   $261.8818   $261.88   $261.90   $261.90  
  Purchase #3 $63.62   9.433%   $69.6213   $69.62   $69.60   $69.60  
  Purchase #4 $69.45   9.517%   $76.0596   $76.06   $76.05   $76.10  
  Purchase #5 $248.59   13.113%   $281.1876   $281.19   $281.20   $281.20  
  Purchase #6 $62.97   9.448%   $68.9194   $68.92   $68.90   $68.90  
  Purchase #7 $23.74   11.161%   $26.3896   $26.39   $26.40   $26.40  
  7 purchase totals = $882.33       $960.8099   $960.81   $960.80   $960.90