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 $214.83   9.629%   $235.516   $235.52   $235.50   $235.50  
  Purchase #2 $91.40   4.550%   $95.5587   $95.56   $95.55   $95.60  
  Purchase #3 $77.66   6.836%   $82.9688   $82.97   $82.95   $83.00  
  Purchase #4 $221.43   3.280%   $228.6929   $228.69   $228.70   $228.70  
  Purchase #5 $50.58   9.833%   $55.5535   $55.55   $55.55   $55.60  
  Purchase #6 $154.59   6.457%   $164.5719   $164.57   $164.55   $164.60  
  Purchase #7 $39.34   9.165%   $42.9455   $42.95   $42.95   $42.90  
  7 purchase totals = $849.83       $905.8073   $905.81   $905.75   $905.90