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 $223.86   11.224%   $248.986   $248.99   $249.00   $249.00  
  Purchase #2 $128.92   11.201%   $143.3603   $143.36   $143.35   $143.40  
  Purchase #3 $53.70   6.230%   $57.0455   $57.05   $57.05   $57.00  
  Purchase #4 $15.42   5.316%   $16.2397   $16.24   $16.25   $16.20  
  Purchase #5 $217.56   11.486%   $242.5489   $242.55   $242.55   $242.50  
  Purchase #6 $239.50   9.362%   $261.922   $261.92   $261.90   $261.90  
  Purchase #7 $219.59   9.457%   $240.3566   $240.36   $240.35   $240.40  
  7 purchase totals = $1,098.55       $1,210.4590   $1,210.47   $1,210.45   $1,210.40