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 $59.59   6.180%   $63.2727   $63.27   $63.25   $63.30  
  Purchase #2 $103.28   4.856%   $108.2953   $108.30   $108.30   $108.30  
  Purchase #3 $15.25   12.340%   $17.1319   $17.13   $17.15   $17.10  
  Purchase #4 $24.64   8.504%   $26.7354   $26.74   $26.75   $26.70  
  Purchase #5 $183.56   5.686%   $193.9972   $194.00   $194.00   $194.00  
  Purchase #6 $30.83   7.127%   $33.0273   $33.03   $33.05   $33.00  
  Purchase #7 $46.95   8.214%   $50.8065   $50.81   $50.80   $50.80  
  7 purchase totals = $464.10       $493.2663   $493.28   $493.30   $493.20