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 $119.88   5.312%   $126.248   $126.25   $126.25   $126.20  
  Purchase #2 $61.93   12.593%   $69.7288   $69.73   $69.75   $69.70  
  Purchase #3 $71.92   9.277%   $78.592   $78.59   $78.60   $78.60  
  Purchase #4 $33.80   8.129%   $36.5476   $36.55   $36.55   $36.50  
  Purchase #5 $124.75   9.737%   $136.8969   $136.90   $136.90   $136.90  
  Purchase #6 $128.45   9.374%   $140.4909   $140.49   $140.50   $140.50  
  Purchase #7 $171.93   9.458%   $188.1911   $188.19   $188.20   $188.20  
  7 purchase totals = $712.66       $776.6953   $776.70   $776.75   $776.60