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 $247.70   5.874%   $262.2499   $262.25   $262.25   $262.20  
  Purchase #2 $78.40   10.787%   $86.857   $86.86   $86.85   $86.90  
  Purchase #3 $77.84   8.667%   $84.5864   $84.59   $84.60   $84.60  
  Purchase #4 $140.78   11.844%   $157.454   $157.45   $157.45   $157.50  
  Purchase #5 $247.73   12.737%   $279.2834   $279.28   $279.30   $279.30  
  Purchase #6 $56.30   8.265%   $60.9532   $60.95   $60.95   $61.00  
  Purchase #7 $174.47   6.395%   $185.6274   $185.63   $185.65   $185.60  
  7 purchase totals = $1,023.22       $1,117.0113   $1,117.01   $1,117.05   $1,117.10