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 $207.45   8.255%   $224.575   $224.58   $224.60   $224.60  
  Purchase #2 $186.53   6.691%   $199.0107   $199.01   $199.00   $199.00  
  Purchase #3 $94.76   13.226%   $107.293   $107.29   $107.30   $107.30  
  Purchase #4 $121.44   5.472%   $128.0852   $128.09   $128.10   $128.10  
  Purchase #5 $23.83   9.696%   $26.1406   $26.14   $26.15   $26.10  
  Purchase #6 $119.72   12.304%   $134.4503   $134.45   $134.45   $134.50  
  Purchase #7 $234.79   11.378%   $261.5044   $261.50   $261.50   $261.50  
  7 purchase totals = $988.52       $1,081.0592   $1,081.06   $1,081.10   $1,081.10