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 $163.51   6.756%   $174.5567   $174.56   $174.55   $174.60  
  Purchase #2 $231.81   8.255%   $250.9459   $250.95   $250.95   $250.90  
  Purchase #3 $83.90   12.117%   $94.0662   $94.07   $94.05   $94.10  
  Purchase #4 $34.54   3.527%   $35.7582   $35.76   $35.75   $35.80  
  Purchase #5 $26.96   7.709%   $29.0383   $29.04   $29.05   $29.00  
  Purchase #6 $87.49   8.605%   $95.0185   $95.02   $95.00   $95.00  
  Purchase #7 $33.99   13.176%   $38.4685   $38.47   $38.45   $38.50  
  7 purchase totals = $662.20       $717.8523   $717.87   $717.80   $717.90