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 $68.91   4.806%   $72.2218   $72.22   $72.20   $72.20  
  Purchase #2 $63.25   8.624%   $68.7047   $68.70   $68.70   $68.70  
  Purchase #3 $25.62   3.459%   $26.5062   $26.51   $26.50   $26.50  
  Purchase #4 $126.64   8.248%   $137.0853   $137.09   $137.10   $137.10  
  Purchase #5 $42.79   8.103%   $46.2573   $46.26   $46.25   $46.30  
  Purchase #6 $92.78   6.225%   $98.5556   $98.56   $98.55   $98.60  
  Purchase #7 $211.92   13.477%   $240.4805   $240.48   $240.50   $240.50  
  7 purchase totals = $631.91       $689.8114   $689.82   $689.80   $689.90