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 $235.74   5.623%   $248.9957   $249.00   $249.00   $249.00  
  Purchase #2 $142.41   10.593%   $157.4955   $157.50   $157.50   $157.50  
  Purchase #3 $137.92   10.303%   $152.1299   $152.13   $152.15   $152.10  
  Purchase #4 $223.83   4.779%   $234.5268   $234.53   $234.55   $234.50  
  Purchase #5 $174.44   4.814%   $182.8375   $182.84   $182.85   $182.80  
  Purchase #6 $41.96   4.754%   $43.9548   $43.95   $43.95   $44.00  
  Purchase #7 $21.74   8.473%   $23.582   $23.58   $23.60   $23.60  
  7 purchase totals = $978.04       $1,043.5222   $1,043.53   $1,043.60   $1,043.50