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 $217.60   10.104%   $239.5863   $239.59   $239.60   $239.60  
  Purchase #2 $219.39   13.658%   $249.3543   $249.35   $249.35   $249.40  
  Purchase #3 $93.97   9.353%   $102.759   $102.76   $102.75   $102.80  
  Purchase #4 $77.32   11.529%   $86.2342   $86.23   $86.25   $86.20  
  Purchase #5 $109.42   3.526%   $113.2781   $113.28   $113.30   $113.30  
  Purchase #6 $144.41   12.385%   $162.2952   $162.30   $162.30   $162.30  
  Purchase #7 $180.37   5.563%   $190.404   $190.40   $190.40   $190.40  
  7 purchase totals = $1,042.48       $1,143.9111   $1,143.91   $1,143.95   $1,144.00