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 $70.59   8.558%   $76.6311   $76.63   $76.65   $76.60  
  Purchase #2 $60.98   7.596%   $65.612   $65.61   $65.60   $65.60  
  Purchase #3 $229.39   3.121%   $236.5493   $236.55   $236.55   $236.50  
  Purchase #4 $239.28   8.299%   $259.1378   $259.14   $259.15   $259.10  
  Purchase #5 $11.79   8.823%   $12.8302   $12.83   $12.85   $12.80  
  Purchase #6 $109.73   7.698%   $118.177   $118.18   $118.20   $118.20  
  Purchase #7 $249.41   9.335%   $272.6924   $272.69   $272.70   $272.70  
  7 purchase totals = $971.17       $1,041.6298   $1,041.63   $1,041.70   $1,041.50