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 $168.83   13.700%   $191.9597   $191.96   $191.95   $192.00  
  Purchase #2 $168.76   3.160%   $174.0928   $174.09   $174.10   $174.10  
  Purchase #3 $102.53   11.627%   $114.4512   $114.45   $114.45   $114.50  
  Purchase #4 $140.60   11.481%   $156.7423   $156.74   $156.75   $156.70  
  Purchase #5 $93.96   3.358%   $97.1152   $97.12   $97.10   $97.10  
  Purchase #6 $165.79   12.409%   $186.3629   $186.36   $186.35   $186.40  
  Purchase #7 $42.59   6.175%   $45.2199   $45.22   $45.20   $45.20  
  7 purchase totals = $883.06       $965.9440   $965.94   $965.90   $966.00