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 $176.44   10.346%   $194.6945   $194.69   $194.70   $194.70  
  Purchase #2 $34.88   10.268%   $38.4615   $38.46   $38.45   $38.50  
  Purchase #3 $61.59   9.226%   $67.2723   $67.27   $67.25   $67.30  
  Purchase #4 $241.98   13.209%   $273.9431   $273.94   $273.95   $273.90  
  Purchase #5 $176.78   4.492%   $184.721   $184.72   $184.70   $184.70  
  Purchase #6 $110.95   12.741%   $125.0861   $125.09   $125.10   $125.10  
  Purchase #7 $196.90   8.448%   $213.5341   $213.53   $213.55   $213.50  
  7 purchase totals = $999.52       $1,097.7126   $1,097.70   $1,097.70   $1,097.70