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 $186.93   10.723%   $206.9745   $206.97   $206.95   $207.00  
  Purchase #2 $245.93   6.396%   $261.6597   $261.66   $261.65   $261.70  
  Purchase #3 $18.28   8.268%   $19.7914   $19.79   $19.80   $19.80  
  Purchase #4 $118.81   12.550%   $133.7207   $133.72   $133.70   $133.70  
  Purchase #5 $55.70   12.531%   $62.6798   $62.68   $62.70   $62.70  
  Purchase #6 $32.73   8.652%   $35.5618   $35.56   $35.55   $35.60  
  Purchase #7 $115.96   9.847%   $127.3786   $127.38   $127.40   $127.40  
  7 purchase totals = $774.34       $847.7665   $847.76   $847.75   $847.90