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 $49.67   6.189%   $52.7441   $52.74   $52.75   $52.70  
  Purchase #2 $153.57   11.758%   $171.6268   $171.63   $171.65   $171.60  
  Purchase #3 $40.31   11.280%   $44.857   $44.86   $44.85   $44.90  
  Purchase #4 $242.34   7.870%   $261.4122   $261.41   $261.40   $261.40  
  Purchase #5 $225.67   9.193%   $246.4158   $246.42   $246.40   $246.40  
  Purchase #6 $78.95   10.156%   $86.9682   $86.97   $86.95   $87.00  
  Purchase #7 $188.80   6.628%   $201.3137   $201.31   $201.30   $201.30  
  7 purchase totals = $979.31       $1,065.3378   $1,065.34   $1,065.30   $1,065.30