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 $59.40   6.170%   $63.065   $63.07   $63.05   $63.10  
  Purchase #2 $213.58   6.532%   $227.531   $227.53   $227.55   $227.50  
  Purchase #3 $93.27   5.817%   $98.6955   $98.70   $98.70   $98.70  
  Purchase #4 $46.45   13.428%   $52.6873   $52.69   $52.70   $52.70  
  Purchase #5 $191.93   11.557%   $214.1114   $214.11   $214.10   $214.10  
  Purchase #6 $71.84   11.176%   $79.8688   $79.87   $79.85   $79.90  
  Purchase #7 $33.59   10.316%   $37.0551   $37.06   $37.05   $37.10  
  7 purchase totals = $710.06       $773.0141   $773.03   $773.00   $773.10