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 $183.47   9.536%   $200.9657   $200.97   $200.95   $201.00  
  Purchase #2 $220.71   13.255%   $249.9651   $249.97   $249.95   $250.00  
  Purchase #3 $114.92   13.276%   $130.1768   $130.18   $130.20   $130.20  
  Purchase #4 $161.67   10.571%   $178.7601   $178.76   $178.75   $178.80  
  Purchase #5 $56.71   11.218%   $63.0717   $63.07   $63.05   $63.10  
  Purchase #6 $71.49   3.585%   $74.0529   $74.05   $74.05   $74.10  
  Purchase #7 $85.47   4.806%   $89.5777   $89.58   $89.60   $89.60  
  7 purchase totals = $894.44       $986.5700   $986.58   $986.55   $986.80