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 $234.70   12.561%   $264.1807   $264.18   $264.20   $264.20  
  Purchase #2 $68.67   7.203%   $73.6163   $73.62   $73.60   $73.60  
  Purchase #3 $71.44   13.509%   $81.0908   $81.09   $81.10   $81.10  
  Purchase #4 $167.68   4.669%   $175.509   $175.51   $175.50   $175.50  
  Purchase #5 $104.88   9.204%   $114.5332   $114.53   $114.55   $114.50  
  Purchase #6 $188.78   4.866%   $197.966   $197.97   $197.95   $198.00  
  Purchase #7 $74.38   7.586%   $80.0225   $80.02   $80.00   $80.00  
  7 purchase totals = $910.53       $986.9185   $986.92   $986.90   $986.90