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 $105.40   8.798%   $114.6731   $114.67   $114.65   $114.70  
  Purchase #2 $184.59   7.133%   $197.7568   $197.76   $197.75   $197.80  
  Purchase #3 $159.45   4.776%   $167.0653   $167.07   $167.05   $167.10  
  Purchase #4 $75.85   12.407%   $85.2607   $85.26   $85.25   $85.30  
  Purchase #5 $113.50   7.714%   $122.2554   $122.26   $122.25   $122.30  
  Purchase #6 $72.61   12.852%   $81.9418   $81.94   $81.95   $81.90  
  Purchase #7 $182.74   4.481%   $190.9286   $190.93   $190.95   $190.90  
  7 purchase totals = $894.14       $959.8817   $959.89   $959.85   $960.00