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 $41.58   12.244%   $46.6711   $46.67   $46.65   $46.70  
  Purchase #2 $101.91   5.153%   $107.1614   $107.16   $107.15   $107.20  
  Purchase #3 $162.41   12.436%   $182.6073   $182.61   $182.60   $182.60  
  Purchase #4 $208.49   6.409%   $221.8521   $221.85   $221.85   $221.90  
  Purchase #5 $152.37   5.169%   $160.246   $160.25   $160.25   $160.20  
  Purchase #6 $53.51   6.306%   $56.8843   $56.88   $56.90   $56.90  
  Purchase #7 $237.80   8.397%   $257.7681   $257.77   $257.75   $257.80  
  7 purchase totals = $958.07       $1,033.1903   $1,033.19   $1,033.15   $1,033.30