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 $185.71   12.408%   $208.7529   $208.75   $208.75   $208.80  
  Purchase #2 $87.80   4.358%   $91.6263   $91.63   $91.65   $91.60  
  Purchase #3 $217.99   13.587%   $247.6083   $247.61   $247.60   $247.60  
  Purchase #4 $245.45   3.441%   $253.8959   $253.90   $253.90   $253.90  
  Purchase #5 $79.64   3.812%   $82.6759   $82.68   $82.70   $82.70  
  Purchase #6 $32.34   13.178%   $36.6018   $36.60   $36.60   $36.60  
  Purchase #7 $239.69   4.546%   $250.5863   $250.59   $250.60   $250.60  
  7 purchase totals = $1,088.62       $1,171.7474   $1,171.76   $1,171.80   $1,171.80