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 $112.74   10.281%   $124.3308   $124.33   $124.35   $124.30  
  Purchase #2 $245.73   6.294%   $261.1962   $261.20   $261.20   $261.20  
  Purchase #3 $107.73   11.450%   $120.0651   $120.07   $120.05   $120.10  
  Purchase #4 $157.54   5.715%   $166.5434   $166.54   $166.55   $166.50  
  Purchase #5 $161.69   7.812%   $174.3212   $174.32   $174.30   $174.30  
  Purchase #6 $88.45   7.335%   $94.9378   $94.94   $94.95   $94.90  
  Purchase #7 $108.86   4.846%   $114.1354   $114.14   $114.15   $114.10  
  7 purchase totals = $982.74       $1,055.5299   $1,055.54   $1,055.55   $1,055.40