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 $65.59   11.351%   $73.0351   $73.04   $73.05   $73.00  
  Purchase #2 $162.34   12.283%   $182.2802   $182.28   $182.30   $182.30  
  Purchase #3 $26.84   12.497%   $30.1942   $30.19   $30.20   $30.20  
  Purchase #4 $48.68   13.398%   $55.2021   $55.20   $55.20   $55.20  
  Purchase #5 $214.87   11.587%   $239.767   $239.77   $239.75   $239.80  
  Purchase #6 $77.48   5.815%   $81.9855   $81.99   $82.00   $82.00  
  Purchase #7 $244.74   7.647%   $263.4553   $263.46   $263.45   $263.50  
  7 purchase totals = $840.54       $925.9194   $925.93   $925.95   $926.00