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 $164.62   4.433%   $171.9176   $171.92   $171.90   $171.90  
  Purchase #2 $190.34   3.473%   $196.9505   $196.95   $196.95   $197.00  
  Purchase #3 $237.96   11.358%   $264.9875   $264.99   $265.00   $265.00  
  Purchase #4 $243.66   8.827%   $265.1679   $265.17   $265.15   $265.20  
  Purchase #5 $68.26   11.700%   $76.2464   $76.25   $76.25   $76.20  
  Purchase #6 $220.76   13.523%   $250.6134   $250.61   $250.60   $250.60  
  Purchase #7 $40.59   5.594%   $42.8606   $42.86   $42.85   $42.90  
  7 purchase totals = $1,166.19       $1,268.7439   $1,268.75   $1,268.70   $1,268.80