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 $148.77   11.471%   $165.8354   $165.84   $165.85   $165.80  
  Purchase #2 $214.81   3.373%   $222.0555   $222.06   $222.05   $222.10  
  Purchase #3 $188.41   8.583%   $204.5812   $204.58   $204.60   $204.60  
  Purchase #4 $225.63   7.677%   $242.9516   $242.95   $242.95   $243.00  
  Purchase #5 $98.54   8.126%   $106.5474   $106.55   $106.55   $106.50  
  Purchase #6 $232.91   12.225%   $261.3832   $261.38   $261.40   $261.40  
  Purchase #7 $179.94   7.177%   $192.8543   $192.85   $192.85   $192.90  
  7 purchase totals = $1,289.01       $1,396.2086   $1,396.21   $1,396.25   $1,396.30