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 $61.39   5.738%   $64.9126   $64.91   $64.90   $64.90  
  Purchase #2 $41.36   9.289%   $45.2019   $45.20   $45.20   $45.20  
  Purchase #3 $101.73   11.548%   $113.4778   $113.48   $113.50   $113.50  
  Purchase #4 $137.87   6.581%   $146.9432   $146.94   $146.95   $146.90  
  Purchase #5 $138.42   11.527%   $154.3757   $154.38   $154.40   $154.40  
  Purchase #6 $78.75   4.663%   $82.4221   $82.42   $82.40   $82.40  
  Purchase #7 $164.57   6.750%   $175.6785   $175.68   $175.70   $175.70  
  7 purchase totals = $724.09       $783.0118   $783.01   $783.05   $783.00