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 $232.37   12.652%   $261.7695   $261.77   $261.75   $261.80  
  Purchase #2 $221.68   11.830%   $247.9047   $247.90   $247.90   $247.90  
  Purchase #3 $164.59   13.383%   $186.6171   $186.62   $186.60   $186.60  
  Purchase #4 $232.36   8.645%   $252.4475   $252.45   $252.45   $252.40  
  Purchase #5 $102.29   4.615%   $107.0107   $107.01   $107.00   $107.00  
  Purchase #6 $132.40   10.710%   $146.58   $146.58   $146.60   $146.60  
  Purchase #7 $173.50   10.725%   $192.1079   $192.11   $192.10   $192.10  
  7 purchase totals = $1,259.19       $1,394.4374   $1,394.44   $1,394.40   $1,394.40