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 $206.38   12.541%   $232.2621   $232.26   $232.25   $232.30  
  Purchase #2 $152.39   8.562%   $165.4376   $165.44   $165.45   $165.40  
  Purchase #3 $44.41   5.544%   $46.8721   $46.87   $46.85   $46.90  
  Purchase #4 $153.81   13.159%   $174.0499   $174.05   $174.05   $174.00  
  Purchase #5 $109.86   6.128%   $116.5922   $116.59   $116.60   $116.60  
  Purchase #6 $101.64   10.711%   $112.5267   $112.53   $112.55   $112.50  
  Purchase #7 $73.88   5.621%   $78.0328   $78.03   $78.05   $78.00  
  7 purchase totals = $842.37       $925.7734   $925.77   $925.80   $925.70