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 $61.98   6.841%   $66.2201   $66.22   $66.20   $66.20  
  Purchase #2 $245.27   6.400%   $260.9673   $260.97   $260.95   $261.00  
  Purchase #3 $177.66   11.568%   $198.2117   $198.21   $198.20   $198.20  
  Purchase #4 $122.48   5.644%   $129.3928   $129.39   $129.40   $129.40  
  Purchase #5 $101.83   3.635%   $105.5315   $105.53   $105.55   $105.50  
  Purchase #6 $22.74   7.350%   $24.4114   $24.41   $24.40   $24.40  
  Purchase #7 $208.69   7.556%   $224.4586   $224.46   $224.45   $224.50  
  7 purchase totals = $940.65       $1,009.1934   $1,009.19   $1,009.15   $1,009.20