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 $241.95   13.690%   $275.073   $275.07   $275.05   $275.10  
  Purchase #2 $93.34   5.758%   $98.7145   $98.71   $98.70   $98.70  
  Purchase #3 $173.74   12.816%   $196.0065   $196.01   $196.00   $196.00  
  Purchase #4 $32.95   10.584%   $36.4374   $36.44   $36.45   $36.40  
  Purchase #5 $208.47   6.457%   $221.9309   $221.93   $221.95   $221.90  
  Purchase #6 $197.73   13.476%   $224.3761   $224.38   $224.40   $224.40  
  Purchase #7 $203.40   7.375%   $218.4008   $218.40   $218.40   $218.40  
  7 purchase totals = $1,151.58       $1,270.9392   $1,270.94   $1,270.95   $1,270.90