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 $139.75   12.377%   $157.0469   $157.05   $157.05   $157.00  
  Purchase #2 $130.81   9.785%   $143.6098   $143.61   $143.60   $143.60  
  Purchase #3 $22.67   4.282%   $23.6407   $23.64   $23.65   $23.60  
  Purchase #4 $141.62   9.117%   $154.5315   $154.53   $154.55   $154.50  
  Purchase #5 $223.53   7.633%   $240.592   $240.59   $240.60   $240.60  
  Purchase #6 $201.59   11.517%   $224.8071   $224.81   $224.80   $224.80  
  Purchase #7 $18.42   9.792%   $20.2237   $20.22   $20.20   $20.20  
  7 purchase totals = $878.39       $964.4517   $964.45   $964.45   $964.30