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 $70.64   7.832%   $76.1725   $76.17   $76.15   $76.20  
  Purchase #2 $177.57   11.562%   $198.1006   $198.10   $198.10   $198.10  
  Purchase #3 $85.66   9.868%   $94.1129   $94.11   $94.10   $94.10  
  Purchase #4 $42.75   9.194%   $46.6804   $46.68   $46.70   $46.70  
  Purchase #5 $87.37   12.822%   $98.5726   $98.57   $98.55   $98.60  
  Purchase #6 $217.68   11.293%   $242.2626   $242.26   $242.25   $242.30  
  Purchase #7 $66.34   10.655%   $73.4085   $73.41   $73.40   $73.40  
  7 purchase totals = $748.01       $829.3101   $829.30   $829.25   $829.40