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 $206.75   3.758%   $214.5197   $214.52   $214.50   $214.50  
  Purchase #2 $141.39   3.673%   $146.5833   $146.58   $146.60   $146.60  
  Purchase #3 $118.86   13.786%   $135.246   $135.25   $135.25   $135.20  
  Purchase #4 $77.57   3.387%   $80.1973   $80.20   $80.20   $80.20  
  Purchase #5 $69.83   12.710%   $78.7054   $78.71   $78.70   $78.70  
  Purchase #6 $148.69   10.630%   $164.4957   $164.50   $164.50   $164.50  
  Purchase #7 $169.54   12.821%   $191.2767   $191.28   $191.30   $191.30  
  7 purchase totals = $932.63       $1,011.0241   $1,011.04   $1,011.05   $1,011.00