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 $196.49   10.568%   $217.2551   $217.26   $217.25   $217.30  
  Purchase #2 $235.92   13.837%   $268.5643   $268.56   $268.55   $268.60  
  Purchase #3 $148.89   7.768%   $160.4558   $160.46   $160.45   $160.50  
  Purchase #4 $208.94   12.516%   $235.0909   $235.09   $235.10   $235.10  
  Purchase #5 $238.72   6.194%   $253.5063   $253.51   $253.50   $253.50  
  Purchase #6 $55.87   3.572%   $57.8657   $57.87   $57.85   $57.90  
  Purchase #7 $21.62   3.859%   $22.4543   $22.45   $22.45   $22.50  
  7 purchase totals = $1,106.45       $1,215.1924   $1,215.20   $1,215.15   $1,215.40