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 $168.58   10.119%   $185.6386   $185.64   $185.65   $185.60  
  Purchase #2 $13.63   4.615%   $14.259   $14.26   $14.25   $14.30  
  Purchase #3 $121.88   11.223%   $135.5586   $135.56   $135.55   $135.60  
  Purchase #4 $220.96   6.782%   $235.9455   $235.95   $235.95   $235.90  
  Purchase #5 $78.25   3.541%   $81.0208   $81.02   $81.00   $81.00  
  Purchase #6 $49.44   13.281%   $56.0061   $56.01   $56.00   $56.00  
  Purchase #7 $34.67   3.854%   $36.0062   $36.01   $36.00   $36.00  
  7 purchase totals = $687.41       $744.4348   $744.45   $744.40   $744.40