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 $239.42   9.377%   $261.8704   $261.87   $261.85   $261.90  
  Purchase #2 $43.71   3.175%   $45.0978   $45.10   $45.10   $45.10  
  Purchase #3 $92.67   9.615%   $101.5802   $101.58   $101.60   $101.60  
  Purchase #4 $209.41   12.128%   $234.8072   $234.81   $234.80   $234.80  
  Purchase #5 $78.27   4.172%   $81.5354   $81.54   $81.55   $81.50  
  Purchase #6 $36.59   12.587%   $41.1956   $41.20   $41.20   $41.20  
  Purchase #7 $24.98   6.129%   $26.511   $26.51   $26.50   $26.50  
  7 purchase totals = $725.05       $792.5976   $792.61   $792.60   $792.60