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 $34.72   11.226%   $38.6177   $38.62   $38.60   $38.60  
  Purchase #2 $218.90   3.776%   $227.1657   $227.17   $227.15   $227.20  
  Purchase #3 $133.39   8.639%   $144.9136   $144.91   $144.90   $144.90  
  Purchase #4 $240.94   11.102%   $267.6892   $267.69   $267.70   $267.70  
  Purchase #5 $23.55   5.813%   $24.919   $24.92   $24.90   $24.90  
  Purchase #6 $184.81   6.481%   $196.7875   $196.79   $196.80   $196.80  
  Purchase #7 $214.48   3.847%   $222.731   $222.73   $222.75   $222.70  
  7 purchase totals = $1,050.79       $1,122.8237   $1,122.83   $1,122.80   $1,122.80