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 $186.83   11.345%   $208.0259   $208.03   $208.05   $208.00  
  Purchase #2 $25.58   3.525%   $26.4817   $26.48   $26.50   $26.50  
  Purchase #3 $239.85   10.667%   $265.4348   $265.43   $265.45   $265.40  
  Purchase #4 $222.26   6.714%   $237.1825   $237.18   $237.20   $237.20  
  Purchase #5 $247.74   8.358%   $268.4461   $268.45   $268.45   $268.40  
  Purchase #6 $127.99   11.348%   $142.5143   $142.51   $142.50   $142.50  
  Purchase #7 $198.28   11.650%   $221.3796   $221.38   $221.40   $221.40  
  7 purchase totals = $1,248.53       $1,369.4649   $1,369.46   $1,369.55   $1,369.40