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 $237.69   13.381%   $269.4953   $269.50   $269.50   $269.50  
  Purchase #2 $73.91   8.582%   $80.253   $80.25   $80.25   $80.30  
  Purchase #3 $20.69   4.859%   $21.6953   $21.70   $21.70   $21.70  
  Purchase #4 $108.94   7.676%   $117.3022   $117.30   $117.30   $117.30  
  Purchase #5 $175.69   12.574%   $197.7813   $197.78   $197.80   $197.80  
  Purchase #6 $158.60   11.247%   $176.4377   $176.44   $176.45   $176.40  
  Purchase #7 $189.54   7.750%   $204.2294   $204.23   $204.25   $204.20  
  7 purchase totals = $965.06       $1,067.1942   $1,067.20   $1,067.25   $1,067.20