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 $239.83   10.357%   $264.6692   $264.67   $264.65   $264.70  
  Purchase #2 $233.95   11.835%   $261.638   $261.64   $261.65   $261.60  
  Purchase #3 $42.25   12.433%   $47.5029   $47.50   $47.50   $47.50  
  Purchase #4 $154.72   13.861%   $176.1657   $176.17   $176.15   $176.20  
  Purchase #5 $201.38   5.424%   $212.3029   $212.30   $212.30   $212.30  
  Purchase #6 $248.64   5.701%   $262.815   $262.82   $262.80   $262.80  
  Purchase #7 $86.66   12.332%   $97.3469   $97.35   $97.35   $97.30  
  7 purchase totals = $1,207.43       $1,322.4406   $1,322.45   $1,322.40   $1,322.40