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 $85.73   11.728%   $95.7844   $95.78   $95.80   $95.80  
  Purchase #2 $236.46   10.655%   $261.6548   $261.65   $261.65   $261.70  
  Purchase #3 $197.74   8.743%   $215.0284   $215.03   $215.05   $215.00  
  Purchase #4 $79.44   4.334%   $82.8829   $82.88   $82.90   $82.90  
  Purchase #5 $80.69   8.431%   $87.493   $87.49   $87.50   $87.50  
  Purchase #6 $186.47   7.476%   $200.4105   $200.41   $200.40   $200.40  
  Purchase #7 $44.42   11.159%   $49.3768   $49.38   $49.40   $49.40  
  7 purchase totals = $910.95       $992.6308   $992.62   $992.70   $992.70