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 $24.74   8.624%   $26.8736   $26.87   $26.85   $26.90  
  Purchase #2 $75.94   9.136%   $82.8779   $82.88   $82.90   $82.90  
  Purchase #3 $68.79   7.292%   $73.8062   $73.81   $73.80   $73.80  
  Purchase #4 $150.77   11.594%   $168.2503   $168.25   $168.25   $168.30  
  Purchase #5 $153.51   13.314%   $173.9483   $173.95   $173.95   $173.90  
  Purchase #6 $24.72   6.434%   $26.3105   $26.31   $26.30   $26.30  
  Purchase #7 $174.58   4.105%   $181.7465   $181.75   $181.75   $181.70  
  7 purchase totals = $673.05       $733.8133   $733.82   $733.80   $733.80