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 $246.63   3.270%   $254.6948   $254.69   $254.70   $254.70  
  Purchase #2 $55.25   11.750%   $61.7419   $61.74   $61.75   $61.70  
  Purchase #3 $118.67   5.676%   $125.4057   $125.41   $125.40   $125.40  
  Purchase #4 $71.46   10.476%   $78.9461   $78.95   $78.95   $78.90  
  Purchase #5 $172.70   11.813%   $193.1011   $193.10   $193.10   $193.10  
  Purchase #6 $197.28   11.249%   $219.472   $219.47   $219.45   $219.50  
  Purchase #7 $82.53   3.216%   $85.1842   $85.18   $85.20   $85.20  
  7 purchase totals = $944.52       $1,018.5458   $1,018.54   $1,018.55   $1,018.50