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 $187.32   3.867%   $194.5637   $194.56   $194.55   $194.60  
  Purchase #2 $92.75   10.449%   $102.4414   $102.44   $102.45   $102.40  
  Purchase #3 $30.49   8.382%   $33.0457   $33.05   $33.05   $33.00  
  Purchase #4 $93.55   3.844%   $97.1461   $97.15   $97.15   $97.10  
  Purchase #5 $184.55   4.162%   $192.231   $192.23   $192.25   $192.20  
  Purchase #6 $125.34   12.269%   $140.718   $140.72   $140.70   $140.70  
  Purchase #7 $114.38   11.680%   $127.7396   $127.74   $127.75   $127.70  
  7 purchase totals = $828.38       $887.8855   $887.89   $887.90   $887.70