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 $239.75   11.506%   $267.3356   $267.34   $267.35   $267.30  
  Purchase #2 $178.93   8.611%   $194.3377   $194.34   $194.35   $194.30  
  Purchase #3 $208.34   5.545%   $219.8925   $219.89   $219.90   $219.90  
  Purchase #4 $125.76   5.318%   $132.4479   $132.45   $132.45   $132.40  
  Purchase #5 $214.88   9.831%   $236.0049   $236.00   $236.00   $236.00  
  Purchase #6 $135.91   9.420%   $148.7127   $148.71   $148.70   $148.70  
  Purchase #7 $5.99   13.595%   $6.8043   $6.80   $6.80   $6.80  
  7 purchase totals = $1,109.56       $1,205.5356   $1,205.53   $1,205.55   $1,205.40