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 $242.83   11.163%   $269.9371   $269.94   $269.95   $269.90  
  Purchase #2 $57.43   7.297%   $61.6207   $61.62   $61.60   $61.60  
  Purchase #3 $46.57   6.516%   $49.6045   $49.60   $49.60   $49.60  
  Purchase #4 $60.25   12.188%   $67.5933   $67.59   $67.60   $67.60  
  Purchase #5 $47.54   11.781%   $53.1407   $53.14   $53.15   $53.10  
  Purchase #6 $182.41   10.698%   $201.9242   $201.92   $201.90   $201.90  
  Purchase #7 $127.88   7.186%   $137.0695   $137.07   $137.05   $137.10  
  7 purchase totals = $764.91       $840.8900   $840.88   $840.85   $840.80