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 $232.90   12.423%   $261.8332   $261.83   $261.85   $261.80  
  Purchase #2 $233.94   12.650%   $263.5334   $263.53   $263.55   $263.50  
  Purchase #3 $15.70   12.750%   $17.7018   $17.70   $17.70   $17.70  
  Purchase #4 $135.63   13.105%   $153.4043   $153.40   $153.40   $153.40  
  Purchase #5 $169.63   11.200%   $188.6286   $188.63   $188.65   $188.60  
  Purchase #6 $19.84   11.415%   $22.1047   $22.10   $22.10   $22.10  
  Purchase #7 $176.40   5.102%   $185.3999   $185.40   $185.40   $185.40  
  7 purchase totals = $984.04       $1,092.6059   $1,092.59   $1,092.65   $1,092.50