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 $205.63   13.189%   $232.7505   $232.75   $232.75   $232.80  
  Purchase #2 $207.91   6.423%   $221.2641   $221.26   $221.25   $221.30  
  Purchase #3 $231.55   9.475%   $253.4894   $253.49   $253.50   $253.50  
  Purchase #4 $146.69   11.425%   $163.4493   $163.45   $163.45   $163.40  
  Purchase #5 $31.70   11.223%   $35.2577   $35.26   $35.25   $35.30  
  Purchase #6 $241.90   4.478%   $252.7323   $252.73   $252.75   $252.70  
  Purchase #7 $201.56   3.218%   $208.0462   $208.05   $208.05   $208.00  
  7 purchase totals = $1,266.94       $1,366.9895   $1,366.99   $1,367.00   $1,367.00