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 $221.37   11.558%   $246.9559   $246.96   $246.95   $247.00  
  Purchase #2 $174.92   8.621%   $189.9999   $190.00   $190.00   $190.00  
  Purchase #3 $20.26   3.276%   $20.9237   $20.92   $20.90   $20.90  
  Purchase #4 $49.25   10.733%   $54.536   $54.54   $54.55   $54.50  
  Purchase #5 $242.89   3.287%   $250.8738   $250.87   $250.85   $250.90  
  Purchase #6 $244.99   8.324%   $265.383   $265.38   $265.40   $265.40  
  Purchase #7 $209.81   10.527%   $231.8967   $231.90   $231.90   $231.90  
  7 purchase totals = $1,163.49       $1,260.5690   $1,260.57   $1,260.55   $1,260.60