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 $228.33   12.532%   $256.9443   $256.94   $256.95   $256.90  
  Purchase #2 $181.76   10.616%   $201.0556   $201.06   $201.05   $201.10  
  Purchase #3 $144.86   9.365%   $158.4261   $158.43   $158.45   $158.40  
  Purchase #4 $249.44   4.635%   $261.0015   $261.00   $261.00   $261.00  
  Purchase #5 $167.70   4.322%   $174.948   $174.95   $174.95   $174.90  
  Purchase #6 $76.33   6.184%   $81.0502   $81.05   $81.05   $81.10  
  Purchase #7 $144.77   12.635%   $163.0617   $163.06   $163.05   $163.10  
  7 purchase totals = $1,193.19       $1,296.4874   $1,296.49   $1,296.50   $1,296.50