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 $87.58   10.247%   $96.5543   $96.55   $96.55   $96.60  
  Purchase #2 $209.30   12.872%   $236.2411   $236.24   $236.25   $236.20  
  Purchase #3 $233.35   12.216%   $261.856   $261.86   $261.85   $261.90  
  Purchase #4 $113.45   7.138%   $121.5481   $121.55   $121.55   $121.50  
  Purchase #5 $235.43   5.522%   $248.4304   $248.43   $248.45   $248.40  
  Purchase #6 $163.82   11.258%   $182.2629   $182.26   $182.25   $182.30  
  Purchase #7 $201.74   9.509%   $220.9235   $220.92   $220.90   $220.90  
  7 purchase totals = $1,244.67       $1,367.8163   $1,367.81   $1,367.80   $1,367.80