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 $54.51   12.478%   $61.3118   $61.31   $61.30   $61.30  
  Purchase #2 $122.76   10.471%   $135.6142   $135.61   $135.60   $135.60  
  Purchase #3 $225.60   10.242%   $248.706   $248.71   $248.70   $248.70  
  Purchase #4 $111.82   11.780%   $124.9924   $124.99   $125.00   $125.00  
  Purchase #5 $29.68   4.157%   $30.9138   $30.91   $30.90   $30.90  
  Purchase #6 $198.87   9.461%   $217.6851   $217.69   $217.70   $217.70  
  Purchase #7 $182.67   8.662%   $198.4929   $198.49   $198.50   $198.50  
  7 purchase totals = $925.91       $1,017.7162   $1,017.71   $1,017.70   $1,017.70