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 $240.90   11.748%   $269.2009   $269.20   $269.20   $269.20  
  Purchase #2 $219.33   6.708%   $234.0427   $234.04   $234.05   $234.00  
  Purchase #3 $12.33   10.563%   $13.6324   $13.63   $13.65   $13.60  
  Purchase #4 $115.79   3.157%   $119.4455   $119.45   $119.45   $119.40  
  Purchase #5 $35.61   6.597%   $37.9592   $37.96   $37.95   $38.00  
  Purchase #6 $171.48   4.626%   $179.4127   $179.41   $179.40   $179.40  
  Purchase #7 $123.58   7.658%   $133.0438   $133.04   $133.05   $133.00  
  7 purchase totals = $919.02       $986.7372   $986.73   $986.75   $986.60