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 $38.45   6.468%   $40.9369   $40.94   $40.95   $40.90  
  Purchase #2 $194.64   6.821%   $207.9164   $207.92   $207.90   $207.90  
  Purchase #3 $246.61   4.685%   $258.1637   $258.16   $258.15   $258.20  
  Purchase #4 $241.95   4.344%   $252.4603   $252.46   $252.45   $252.50  
  Purchase #5 $89.71   12.836%   $101.2252   $101.23   $101.25   $101.20  
  Purchase #6 $240.88   5.783%   $254.8101   $254.81   $254.80   $254.80  
  Purchase #7 $87.81   12.167%   $98.4938   $98.49   $98.50   $98.50  
  7 purchase totals = $1,140.05       $1,214.0064   $1,214.01   $1,214.00   $1,214.00