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 $240.81   9.113%   $262.755   $262.76   $262.75   $262.80  
  Purchase #2 $135.78   12.646%   $152.9507   $152.95   $152.95   $153.00  
  Purchase #3 $140.41   12.750%   $158.3123   $158.31   $158.30   $158.30  
  Purchase #4 $57.67   12.556%   $64.911   $64.91   $64.90   $64.90  
  Purchase #5 $108.34   4.463%   $113.1752   $113.18   $113.20   $113.20  
  Purchase #6 $59.70   12.722%   $67.295   $67.30   $67.30   $67.30  
  Purchase #7 $234.87   4.677%   $245.8549   $245.85   $245.85   $245.90  
  7 purchase totals = $977.58       $1,065.2541   $1,065.26   $1,065.25   $1,065.40