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 $74.64   11.208%   $83.0057   $83.01   $83.00   $83.00  
  Purchase #2 $174.40   13.354%   $197.6894   $197.69   $197.70   $197.70  
  Purchase #3 $214.38   12.692%   $241.5891   $241.59   $241.60   $241.60  
  Purchase #4 $248.25   5.143%   $261.0175   $261.02   $261.00   $261.00  
  Purchase #5 $49.26   9.785%   $54.0801   $54.08   $54.10   $54.10  
  Purchase #6 $221.61   7.147%   $237.4485   $237.45   $237.45   $237.40  
  Purchase #7 $57.58   9.812%   $63.2297   $63.23   $63.25   $63.20  
  7 purchase totals = $1,040.12       $1,138.0600   $1,138.07   $1,138.10   $1,138.00