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 $66.99   10.341%   $73.9174   $73.92   $73.90   $73.90  
  Purchase #2 $122.65   3.198%   $126.5723   $126.57   $126.55   $126.60  
  Purchase #3 $114.87   4.647%   $120.208   $120.21   $120.20   $120.20  
  Purchase #4 $91.66   6.182%   $97.3264   $97.33   $97.35   $97.30  
  Purchase #5 $249.75   10.697%   $276.4658   $276.47   $276.45   $276.50  
  Purchase #6 $62.48   13.866%   $71.1435   $71.14   $71.15   $71.10  
  Purchase #7 $227.31   9.243%   $248.3203   $248.32   $248.30   $248.30  
  7 purchase totals = $935.71       $1,013.9537   $1,013.96   $1,013.90   $1,013.90