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 $96.83   6.636%   $103.2556   $103.26   $103.25   $103.30  
  Purchase #2 $168.43   3.282%   $173.9579   $173.96   $173.95   $174.00  
  Purchase #3 $73.41   4.314%   $76.5769   $76.58   $76.60   $76.60  
  Purchase #4 $250.55   5.783%   $265.0393   $265.04   $265.05   $265.00  
  Purchase #5 $234.91   5.828%   $248.6006   $248.60   $248.60   $248.60  
  Purchase #6 $24.59   12.641%   $27.6984   $27.70   $27.70   $27.70  
  Purchase #7 $49.45   11.270%   $55.023   $55.02   $55.00   $55.00  
  7 purchase totals = $898.17       $950.1517   $950.16   $950.15   $950.20