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 $60.34   9.307%   $65.9558   $65.96   $65.95   $66.00  
  Purchase #2 $72.57   9.767%   $79.6579   $79.66   $79.65   $79.70  
  Purchase #3 $47.90   10.442%   $52.9017   $52.90   $52.90   $52.90  
  Purchase #4 $227.54   8.586%   $247.0766   $247.08   $247.10   $247.10  
  Purchase #5 $183.26   13.493%   $207.9873   $207.99   $208.00   $208.00  
  Purchase #6 $172.47   10.593%   $190.7397   $190.74   $190.75   $190.70  
  Purchase #7 $19.58   13.584%   $22.2397   $22.24   $22.25   $22.20  
  7 purchase totals = $783.66       $866.5587   $866.57   $866.60   $866.60