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 $110.88   13.664%   $126.0306   $126.03   $126.05   $126.00  
  Purchase #2 $245.42   8.622%   $266.5801   $266.58   $266.60   $266.60  
  Purchase #3 $203.34   5.855%   $215.2456   $215.25   $215.25   $215.20  
  Purchase #4 $228.25   7.468%   $245.2957   $245.30   $245.30   $245.30  
  Purchase #5 $210.91   12.853%   $238.0183   $238.02   $238.00   $238.00  
  Purchase #6 $221.92   6.791%   $236.9906   $236.99   $237.00   $237.00  
  Purchase #7 $59.75   12.793%   $67.3938   $67.39   $67.40   $67.40  
  7 purchase totals = $1,280.47       $1,395.5547   $1,395.56   $1,395.60   $1,395.50