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 $14.66   9.573%   $16.0634   $16.06   $16.05   $16.10  
  Purchase #2 $184.25   4.608%   $192.7402   $192.74   $192.75   $192.70  
  Purchase #3 $156.44   9.241%   $170.8966   $170.90   $170.90   $170.90  
  Purchase #4 $219.93   7.500%   $236.4248   $236.42   $236.40   $236.40  
  Purchase #5 $109.76   4.221%   $114.393   $114.39   $114.40   $114.40  
  Purchase #6 $69.69   9.388%   $76.2325   $76.23   $76.25   $76.20  
  Purchase #7 $27.71   3.411%   $28.6552   $28.66   $28.65   $28.70  
  7 purchase totals = $782.44       $835.4057   $835.40   $835.40   $835.40