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 $97.82   12.352%   $109.9027   $109.90   $109.90   $109.90  
  Purchase #2 $188.68   4.231%   $196.6631   $196.66   $196.65   $196.70  
  Purchase #3 $11.25   4.420%   $11.7473   $11.75   $11.75   $11.70  
  Purchase #4 $15.84   11.310%   $17.6315   $17.63   $17.65   $17.60  
  Purchase #5 $250.67   7.550%   $269.5956   $269.60   $269.60   $269.60  
  Purchase #6 $250.25   4.376%   $261.2009   $261.20   $261.20   $261.20  
  Purchase #7 $51.65   7.539%   $55.5439   $55.54   $55.55   $55.50  
  7 purchase totals = $866.16       $922.2850   $922.28   $922.30   $922.20