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 $250.29   4.517%   $261.5956   $261.60   $261.60   $261.60  
  Purchase #2 $50.29   12.864%   $56.7593   $56.76   $56.75   $56.80  
  Purchase #3 $166.33   4.161%   $173.251   $173.25   $173.25   $173.30  
  Purchase #4 $107.99   12.299%   $121.2717   $121.27   $121.25   $121.30  
  Purchase #5 $237.92   5.740%   $251.5766   $251.58   $251.60   $251.60  
  Purchase #6 $70.51   10.509%   $77.9199   $77.92   $77.90   $77.90  
  Purchase #7 $84.65   12.671%   $95.376   $95.38   $95.40   $95.40  
  7 purchase totals = $967.98       $1,037.7501   $1,037.76   $1,037.75   $1,037.90