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 $67.26   5.455%   $70.929   $70.93   $70.95   $70.90  
  Purchase #2 $27.33   10.739%   $30.265   $30.27   $30.25   $30.30  
  Purchase #3 $185.43   6.808%   $198.0541   $198.05   $198.05   $198.10  
  Purchase #4 $230.50   10.699%   $255.1612   $255.16   $255.15   $255.20  
  Purchase #5 $156.80   5.368%   $165.217   $165.22   $165.20   $165.20  
  Purchase #6 $44.80   8.266%   $48.5032   $48.50   $48.50   $48.50  
  Purchase #7 $47.97   11.670%   $53.5681   $53.57   $53.55   $53.60  
  7 purchase totals = $760.09       $821.6976   $821.70   $821.65   $821.80