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 $214.89   10.242%   $236.899   $236.90   $236.90   $236.90  
  Purchase #2 $181.40   6.587%   $193.3488   $193.35   $193.35   $193.30  
  Purchase #3 $212.34   12.192%   $238.2285   $238.23   $238.25   $238.20  
  Purchase #4 $136.32   3.461%   $141.038   $141.04   $141.05   $141.00  
  Purchase #5 $27.75   8.135%   $30.0075   $30.01   $30.00   $30.00  
  Purchase #6 $223.67   13.559%   $253.9974   $254.00   $254.00   $254.00  
  Purchase #7 $164.28   6.202%   $174.4686   $174.47   $174.45   $174.50  
  7 purchase totals = $1,160.65       $1,267.9878   $1,268.00   $1,268.00   $1,267.90