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 $107.56   6.535%   $114.589   $114.59   $114.60   $114.60  
  Purchase #2 $207.37   9.311%   $226.6782   $226.68   $226.70   $226.70  
  Purchase #3 $37.84   3.309%   $39.0921   $39.09   $39.10   $39.10  
  Purchase #4 $115.34   9.621%   $126.4369   $126.44   $126.45   $126.40  
  Purchase #5 $118.68   10.868%   $131.5781   $131.58   $131.60   $131.60  
  Purchase #6 $44.31   6.632%   $47.2486   $47.25   $47.25   $47.20  
  Purchase #7 $127.90   7.844%   $137.9325   $137.93   $137.95   $137.90  
  7 purchase totals = $759.00       $823.5554   $823.56   $823.65   $823.50