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 $111.62   12.161%   $125.1941   $125.19   $125.20   $125.20  
  Purchase #2 $47.88   4.577%   $50.0715   $50.07   $50.05   $50.10  
  Purchase #3 $131.98   12.656%   $148.6834   $148.68   $148.70   $148.70  
  Purchase #4 $249.54   5.245%   $262.6284   $262.63   $262.65   $262.60  
  Purchase #5 $220.76   9.598%   $241.9485   $241.95   $241.95   $241.90  
  Purchase #6 $100.36   5.267%   $105.646   $105.65   $105.65   $105.60  
  Purchase #7 $103.45   13.535%   $117.452   $117.45   $117.45   $117.50  
  7 purchase totals = $965.59       $1,051.6239   $1,051.62   $1,051.65   $1,051.60