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 $76.72   9.393%   $83.9263   $83.93   $83.95   $83.90  
  Purchase #2 $103.71   11.529%   $115.6667   $115.67   $115.65   $115.70  
  Purchase #3 $243.95   3.610%   $252.7566   $252.76   $252.75   $252.80  
  Purchase #4 $242.97   3.193%   $250.728   $250.73   $250.75   $250.70  
  Purchase #5 $139.61   7.160%   $149.6061   $149.61   $149.60   $149.60  
  Purchase #6 $141.69   12.841%   $159.8844   $159.88   $159.90   $159.90  
  Purchase #7 $239.32   4.274%   $249.5485   $249.55   $249.55   $249.50  
  7 purchase totals = $1,187.97       $1,262.1166   $1,262.13   $1,262.15   $1,262.10