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 $51.81   11.371%   $57.7013   $57.70   $57.70   $57.70  
  Purchase #2 $227.49   8.470%   $246.7584   $246.76   $246.75   $246.80  
  Purchase #3 $250.52   3.789%   $260.0122   $260.01   $260.00   $260.00  
  Purchase #4 $126.77   11.371%   $141.185   $141.19   $141.20   $141.20  
  Purchase #5 $10.98   5.756%   $11.612   $11.61   $11.60   $11.60  
  Purchase #6 $234.97   4.536%   $245.6282   $245.63   $245.65   $245.60  
  Purchase #7 $58.71   5.228%   $61.7794   $61.78   $61.80   $61.80  
  7 purchase totals = $961.25       $1,024.6765   $1,024.68   $1,024.70   $1,024.70