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 $242.25   4.867%   $254.0403   $254.04   $254.05   $254.00  
  Purchase #2 $177.38   13.693%   $201.6686   $201.67   $201.65   $201.70  
  Purchase #3 $94.34   11.817%   $105.4882   $105.49   $105.50   $105.50  
  Purchase #4 $176.96   11.490%   $197.2927   $197.29   $197.30   $197.30  
  Purchase #5 $73.42   6.188%   $77.9632   $77.96   $77.95   $78.00  
  Purchase #6 $54.48   5.732%   $57.6028   $57.60   $57.60   $57.60  
  Purchase #7 $17.71   12.860%   $19.9875   $19.99   $20.00   $20.00  
  7 purchase totals = $836.54       $914.0433   $914.04   $914.05   $914.10