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 $136.55   12.673%   $153.855   $153.86   $153.85   $153.90  
  Purchase #2 $46.61   4.235%   $48.5839   $48.58   $48.60   $48.60  
  Purchase #3 $65.47   6.821%   $69.9357   $69.94   $69.95   $69.90  
  Purchase #4 $248.36   5.553%   $262.1514   $262.15   $262.15   $262.20  
  Purchase #5 $79.38   5.440%   $83.6983   $83.70   $83.70   $83.70  
  Purchase #6 $38.95   12.141%   $43.6789   $43.68   $43.70   $43.70  
  Purchase #7 $86.39   6.559%   $92.0563   $92.06   $92.05   $92.10  
  7 purchase totals = $701.71       $753.9595   $753.97   $754.00   $754.10