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 $228.87   5.541%   $241.5517   $241.55   $241.55   $241.60  
  Purchase #2 $15.34   12.549%   $17.265   $17.27   $17.25   $17.30  
  Purchase #3 $165.77   12.159%   $185.926   $185.93   $185.95   $185.90  
  Purchase #4 $119.59   12.594%   $134.6512   $134.65   $134.65   $134.70  
  Purchase #5 $197.56   5.787%   $208.9928   $208.99   $209.00   $209.00  
  Purchase #6 $64.32   6.432%   $68.4571   $68.46   $68.45   $68.50  
  Purchase #7 $23.90   13.178%   $27.0495   $27.05   $27.05   $27.00  
  7 purchase totals = $815.35       $883.8933   $883.90   $883.90   $884.00