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 $186.98   8.174%   $202.2637   $202.26   $202.25   $202.30  
  Purchase #2 $108.27   11.615%   $120.8456   $120.85   $120.85   $120.80  
  Purchase #3 $197.46   5.787%   $208.887   $208.89   $208.90   $208.90  
  Purchase #4 $213.29   12.703%   $240.3842   $240.38   $240.40   $240.40  
  Purchase #5 $161.40   8.685%   $175.4176   $175.42   $175.40   $175.40  
  Purchase #6 $133.78   5.855%   $141.6128   $141.61   $141.60   $141.60  
  Purchase #7 $197.76   5.410%   $208.4588   $208.46   $208.45   $208.50  
  7 purchase totals = $1,198.94       $1,297.8697   $1,297.87   $1,297.85   $1,297.90