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 $232.49   11.188%   $258.501   $258.50   $258.50   $258.50  
  Purchase #2 $105.59   13.555%   $119.9027   $119.90   $119.90   $119.90  
  Purchase #3 $53.46   5.830%   $56.5767   $56.58   $56.60   $56.60  
  Purchase #4 $32.57   5.599%   $34.3936   $34.39   $34.40   $34.40  
  Purchase #5 $222.33   9.217%   $242.8222   $242.82   $242.80   $242.80  
  Purchase #6 $164.36   7.274%   $176.3155   $176.32   $176.30   $176.30  
  Purchase #7 $197.26   8.348%   $213.7273   $213.73   $213.75   $213.70  
  7 purchase totals = $1,008.06       $1,102.2390   $1,102.24   $1,102.25   $1,102.20