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 $241.73   10.122%   $266.1979   $266.20   $266.20   $266.20  
  Purchase #2 $102.85   11.117%   $114.2838   $114.28   $114.30   $114.30  
  Purchase #3 $55.78   5.243%   $58.7045   $58.70   $58.70   $58.70  
  Purchase #4 $6.48   9.139%   $7.0722   $7.07   $7.05   $7.10  
  Purchase #5 $54.88   4.105%   $57.1328   $57.13   $57.15   $57.10  
  Purchase #6 $201.81   13.455%   $228.9635   $228.96   $228.95   $229.00  
  Purchase #7 $60.58   6.332%   $64.4159   $64.42   $64.40   $64.40  
  7 purchase totals = $724.11       $796.7706   $796.76   $796.75   $796.80