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 $60.54   4.495%   $63.2613   $63.26   $63.25   $63.30  
  Purchase #2 $151.72   8.303%   $164.3173   $164.32   $164.30   $164.30  
  Purchase #3 $183.28   8.365%   $198.6114   $198.61   $198.60   $198.60  
  Purchase #4 $188.73   4.438%   $197.1058   $197.11   $197.10   $197.10  
  Purchase #5 $132.65   9.217%   $144.8764   $144.88   $144.90   $144.90  
  Purchase #6 $47.40   13.856%   $53.9677   $53.97   $53.95   $54.00  
  Purchase #7 $73.31   10.509%   $81.0141   $81.01   $81.00   $81.00  
  7 purchase totals = $837.63       $903.1540   $903.16   $903.10   $903.20