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 $136.68   5.144%   $143.7108   $143.71   $143.70   $143.70  
  Purchase #2 $164.42   8.692%   $178.7114   $178.71   $178.70   $178.70  
  Purchase #3 $69.63   10.133%   $76.6856   $76.69   $76.70   $76.70  
  Purchase #4 $174.50   12.745%   $196.74   $196.74   $196.75   $196.70  
  Purchase #5 $140.48   7.859%   $151.5203   $151.52   $151.50   $151.50  
  Purchase #6 $223.33   5.256%   $235.0682   $235.07   $235.05   $235.10  
  Purchase #7 $46.33   9.797%   $50.869   $50.87   $50.85   $50.90  
  7 purchase totals = $955.37       $1,033.3053   $1,033.31   $1,033.25   $1,033.30