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 $67.70   6.292%   $71.9597   $71.96   $71.95   $72.00  
  Purchase #2 $183.38   8.873%   $199.6513   $199.65   $199.65   $199.70  
  Purchase #3 $71.66   6.667%   $76.4376   $76.44   $76.45   $76.40  
  Purchase #4 $208.45   13.719%   $237.0473   $237.05   $237.05   $237.00  
  Purchase #5 $138.85   12.700%   $156.484   $156.48   $156.50   $156.50  
  Purchase #6 $11.75   8.475%   $12.7458   $12.75   $12.75   $12.70  
  Purchase #7 $197.41   13.613%   $224.2834   $224.28   $224.30   $224.30  
  7 purchase totals = $879.20       $978.6091   $978.61   $978.65   $978.60