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 $244.81   11.536%   $273.0513   $273.05   $273.05   $273.10  
  Purchase #2 $229.80   13.861%   $261.6526   $261.65   $261.65   $261.70  
  Purchase #3 $78.73   8.105%   $85.1111   $85.11   $85.10   $85.10  
  Purchase #4 $177.45   3.705%   $184.0245   $184.02   $184.00   $184.00  
  Purchase #5 $77.34   5.245%   $81.3965   $81.40   $81.40   $81.40  
  Purchase #6 $59.57   5.264%   $62.7058   $62.71   $62.70   $62.70  
  Purchase #7 $108.56   5.563%   $114.5992   $114.60   $114.60   $114.60  
  7 purchase totals = $976.26       $1,062.5410   $1,062.54   $1,062.50   $1,062.60