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 $206.66   9.675%   $226.6544   $226.65   $226.65   $226.70  
  Purchase #2 $237.39   13.821%   $270.1997   $270.20   $270.20   $270.20  
  Purchase #3 $49.59   5.495%   $52.315   $52.32   $52.30   $52.30  
  Purchase #4 $61.29   5.254%   $64.5102   $64.51   $64.50   $64.50  
  Purchase #5 $175.89   8.379%   $190.6278   $190.63   $190.65   $190.60  
  Purchase #6 $122.52   13.709%   $139.3163   $139.32   $139.30   $139.30  
  Purchase #7 $77.33   6.354%   $82.2435   $82.24   $82.25   $82.20  
  7 purchase totals = $930.67       $1,025.8669   $1,025.87   $1,025.85   $1,025.80