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 $76.86   11.553%   $85.7396   $85.74   $85.75   $85.70  
  Purchase #2 $232.62   12.274%   $261.1718   $261.17   $261.15   $261.20  
  Purchase #3 $171.40   8.623%   $186.1798   $186.18   $186.20   $186.20  
  Purchase #4 $74.89   8.468%   $81.2317   $81.23   $81.25   $81.20  
  Purchase #5 $156.93   11.316%   $174.6882   $174.69   $174.70   $174.70  
  Purchase #6 $21.40   13.229%   $24.231   $24.23   $24.25   $24.20  
  Purchase #7 $105.66   12.367%   $118.727   $118.73   $118.75   $118.70  
  7 purchase totals = $839.76       $931.9691   $931.97   $932.05   $931.90