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 $214.53   8.174%   $232.0657   $232.07   $232.05   $232.10  
  Purchase #2 $8.84   7.529%   $9.5056   $9.51   $9.50   $9.50  
  Purchase #3 $164.65   7.582%   $177.1338   $177.13   $177.15   $177.10  
  Purchase #4 $120.92   11.598%   $134.9443   $134.94   $134.95   $134.90  
  Purchase #5 $210.76   13.494%   $239.2   $239.20   $239.20   $239.20  
  Purchase #6 $103.94   10.556%   $114.9119   $114.91   $114.90   $114.90  
  Purchase #7 $70.54   8.582%   $76.5937   $76.59   $76.60   $76.60  
  7 purchase totals = $894.18       $984.3550   $984.35   $984.35   $984.30