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 $179.41   3.827%   $186.276   $186.28   $186.30   $186.30  
  Purchase #2 $62.36   6.246%   $66.255   $66.26   $66.25   $66.30  
  Purchase #3 $115.70   6.391%   $123.0944   $123.09   $123.10   $123.10  
  Purchase #4 $207.47   3.780%   $215.3124   $215.31   $215.30   $215.30  
  Purchase #5 $38.47   11.565%   $42.9191   $42.92   $42.90   $42.90  
  Purchase #6 $198.29   7.694%   $213.5464   $213.55   $213.55   $213.50  
  Purchase #7 $242.92   7.451%   $261.02   $261.02   $261.00   $261.00  
  7 purchase totals = $1,044.62       $1,108.4233   $1,108.43   $1,108.40   $1,108.40