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 $238.40   11.647%   $266.1664   $266.17   $266.15   $266.20  
  Purchase #2 $136.29   11.817%   $152.3954   $152.40   $152.40   $152.40  
  Purchase #3 $95.90   12.641%   $108.0227   $108.02   $108.00   $108.00  
  Purchase #4 $22.61   5.377%   $23.8257   $23.83   $23.85   $23.80  
  Purchase #5 $38.40   10.581%   $42.4631   $42.46   $42.45   $42.50  
  Purchase #6 $164.97   3.486%   $170.7209   $170.72   $170.70   $170.70  
  Purchase #7 $246.76   5.727%   $260.8919   $260.89   $260.90   $260.90  
  7 purchase totals = $943.33       $1,024.4861   $1,024.49   $1,024.45   $1,024.50