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 $187.26   11.455%   $208.7106   $208.71   $208.70   $208.70  
  Purchase #2 $31.61   9.394%   $34.5794   $34.58   $34.60   $34.60  
  Purchase #3 $206.70   7.137%   $221.4522   $221.45   $221.45   $221.50  
  Purchase #4 $156.42   8.247%   $169.32   $169.32   $169.30   $169.30  
  Purchase #5 $58.41   12.660%   $65.8047   $65.80   $65.80   $65.80  
  Purchase #6 $239.54   5.501%   $252.7171   $252.72   $252.70   $252.70  
  Purchase #7 $241.51   11.366%   $268.96   $268.96   $268.95   $269.00  
  7 purchase totals = $1,121.45       $1,221.5440   $1,221.54   $1,221.50   $1,221.60