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 $96.81   11.155%   $107.6092   $107.61   $107.60   $107.60  
  Purchase #2 $37.99   9.511%   $41.6032   $41.60   $41.60   $41.60  
  Purchase #3 $158.95   3.765%   $164.9345   $164.93   $164.95   $164.90  
  Purchase #4 $242.90   4.795%   $254.5471   $254.55   $254.55   $254.50  
  Purchase #5 $141.67   6.766%   $151.2554   $151.26   $151.25   $151.30  
  Purchase #6 $36.63   4.460%   $38.2637   $38.26   $38.25   $38.30  
  Purchase #7 $179.28   10.671%   $198.411   $198.41   $198.40   $198.40  
  7 purchase totals = $894.23       $956.6241   $956.62   $956.60   $956.60