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 $23.66   12.303%   $26.5709   $26.57   $26.55   $26.60  
  Purchase #2 $216.79   6.116%   $230.0489   $230.05   $230.05   $230.00  
  Purchase #3 $237.69   6.395%   $252.8903   $252.89   $252.90   $252.90  
  Purchase #4 $198.85   11.146%   $221.0138   $221.01   $221.00   $221.00  
  Purchase #5 $97.56   5.327%   $102.757   $102.76   $102.75   $102.80  
  Purchase #6 $170.32   13.767%   $193.768   $193.77   $193.75   $193.80  
  Purchase #7 $122.32   12.403%   $137.4913   $137.49   $137.50   $137.50  
  7 purchase totals = $1,067.19       $1,164.5402   $1,164.54   $1,164.50   $1,164.60