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 $241.84   11.394%   $269.3952   $269.40   $269.40   $269.40  
  Purchase #2 $46.85   8.228%   $50.7048   $50.70   $50.70   $50.70  
  Purchase #3 $151.93   5.698%   $160.587   $160.59   $160.60   $160.60  
  Purchase #4 $36.62   4.794%   $38.3756   $38.38   $38.40   $38.40  
  Purchase #5 $71.92   6.248%   $76.4136   $76.41   $76.40   $76.40  
  Purchase #6 $127.31   9.867%   $139.8717   $139.87   $139.85   $139.90  
  Purchase #7 $230.67   9.540%   $252.6759   $252.68   $252.70   $252.70  
  7 purchase totals = $907.14       $988.0238   $988.03   $988.05   $988.10