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 $242.38   10.636%   $268.1595   $268.16   $268.15   $268.20  
  Purchase #2 $163.50   7.869%   $176.3658   $176.37   $176.35   $176.40  
  Purchase #3 $179.61   10.743%   $198.9055   $198.91   $198.90   $198.90  
  Purchase #4 $142.57   8.681%   $154.9465   $154.95   $154.95   $154.90  
  Purchase #5 $196.38   5.723%   $207.6188   $207.62   $207.60   $207.60  
  Purchase #6 $232.97   9.162%   $254.3147   $254.31   $254.30   $254.30  
  Purchase #7 $169.36   7.612%   $182.2517   $182.25   $182.25   $182.30  
  7 purchase totals = $1,326.77       $1,442.5625   $1,442.57   $1,442.50   $1,442.60