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 $248.87   5.621%   $262.859   $262.86   $262.85   $262.90  
  Purchase #2 $62.67   5.197%   $65.927   $65.93   $65.95   $65.90  
  Purchase #3 $229.83   13.612%   $261.1145   $261.11   $261.10   $261.10  
  Purchase #4 $205.41   11.270%   $228.5597   $228.56   $228.55   $228.60  
  Purchase #5 $49.26   11.839%   $55.0919   $55.09   $55.10   $55.10  
  Purchase #6 $138.30   9.205%   $151.0305   $151.03   $151.05   $151.00  
  Purchase #7 $186.76   6.567%   $199.0245   $199.02   $199.00   $199.00  
  7 purchase totals = $1,121.10       $1,223.6071   $1,223.60   $1,223.60   $1,223.60