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 $213.83   10.556%   $236.4019   $236.40   $236.40   $236.40  
  Purchase #2 $174.81   4.656%   $182.9492   $182.95   $182.95   $182.90  
  Purchase #3 $248.39   8.874%   $270.4321   $270.43   $270.45   $270.40  
  Purchase #4 $104.82   5.599%   $110.6889   $110.69   $110.70   $110.70  
  Purchase #5 $106.75   12.321%   $119.9027   $119.90   $119.90   $119.90  
  Purchase #6 $62.46   3.466%   $64.6249   $64.62   $64.60   $64.60  
  Purchase #7 $88.64   11.567%   $98.893   $98.89   $98.90   $98.90  
  7 purchase totals = $999.70       $1,083.8927   $1,083.88   $1,083.90   $1,083.80