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 $41.87   12.555%   $47.1268   $47.13   $47.15   $47.10  
  Purchase #2 $226.65   5.247%   $238.5423   $238.54   $238.55   $238.50  
  Purchase #3 $103.66   10.160%   $114.1919   $114.19   $114.20   $114.20  
  Purchase #4 $143.72   8.558%   $156.0196   $156.02   $156.00   $156.00  
  Purchase #5 $132.94   3.127%   $137.097   $137.10   $137.10   $137.10  
  Purchase #6 $70.87   3.577%   $73.405   $73.41   $73.40   $73.40  
  Purchase #7 $153.46   8.122%   $165.924   $165.92   $165.90   $165.90  
  7 purchase totals = $873.17       $932.3066   $932.31   $932.30   $932.20