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 $31.96   6.259%   $33.9604   $33.96   $33.95   $34.00  
  Purchase #2 $81.56   3.274%   $84.2303   $84.23   $84.25   $84.20  
  Purchase #3 $136.41   5.230%   $143.5442   $143.54   $143.55   $143.50  
  Purchase #4 $234.82   6.298%   $249.609   $249.61   $249.60   $249.60  
  Purchase #5 $73.38   6.476%   $78.1321   $78.13   $78.15   $78.10  
  Purchase #6 $100.62   6.444%   $107.104   $107.10   $107.10   $107.10  
  Purchase #7 $229.90   4.168%   $239.4822   $239.48   $239.50   $239.50  
  7 purchase totals = $888.65       $936.0622   $936.05   $936.10   $936.00