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 $69.71   5.229%   $73.3551   $73.36   $73.35   $73.40  
  Purchase #2 $183.95   12.151%   $206.3018   $206.30   $206.30   $206.30  
  Purchase #3 $63.42   10.792%   $70.2643   $70.26   $70.25   $70.30  
  Purchase #4 $9.66   5.291%   $10.1711   $10.17   $10.15   $10.20  
  Purchase #5 $214.98   4.713%   $225.112   $225.11   $225.10   $225.10  
  Purchase #6 $14.88   8.267%   $16.1101   $16.11   $16.10   $16.10  
  Purchase #7 $164.90   4.271%   $171.9429   $171.94   $171.95   $171.90  
  7 purchase totals = $721.50       $773.2573   $773.25   $773.20   $773.30