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 $180.70   3.272%   $186.6125   $186.61   $186.60   $186.60  
  Purchase #2 $233.26   8.391%   $252.8328   $252.83   $252.85   $252.80  
  Purchase #3 $6.34   6.556%   $6.7557   $6.76   $6.75   $6.80  
  Purchase #4 $207.49   3.280%   $214.2957   $214.30   $214.30   $214.30  
  Purchase #5 $226.38   13.259%   $256.3957   $256.40   $256.40   $256.40  
  Purchase #6 $27.40   11.800%   $30.6332   $30.63   $30.65   $30.60  
  Purchase #7 $13.88   3.273%   $14.3343   $14.33   $14.35   $14.30  
  7 purchase totals = $895.45       $961.8599   $961.86   $961.90   $961.80