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 $209.56   11.696%   $234.0701   $234.07   $234.05   $234.10  
  Purchase #2 $66.72   6.797%   $71.255   $71.26   $71.25   $71.30  
  Purchase #3 $69.86   9.490%   $76.4897   $76.49   $76.50   $76.50  
  Purchase #4 $210.74   10.703%   $233.2955   $233.30   $233.30   $233.30  
  Purchase #5 $44.44   4.545%   $46.4598   $46.46   $46.45   $46.50  
  Purchase #6 $217.45   10.430%   $240.13   $240.13   $240.15   $240.10  
  Purchase #7 $21.45   5.361%   $22.5999   $22.60   $22.60   $22.60  
  7 purchase totals = $840.22       $924.3000   $924.31   $924.30   $924.40