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 $59.53   10.769%   $65.9408   $65.94   $65.95   $65.90  
  Purchase #2 $244.75   5.498%   $258.2064   $258.21   $258.20   $258.20  
  Purchase #3 $39.97   11.715%   $44.6525   $44.65   $44.65   $44.70  
  Purchase #4 $85.40   12.871%   $96.3918   $96.39   $96.40   $96.40  
  Purchase #5 $38.99   7.414%   $41.8807   $41.88   $41.90   $41.90  
  Purchase #6 $200.89   11.716%   $224.4263   $224.43   $224.45   $224.40  
  Purchase #7 $12.81   4.685%   $13.4101   $13.41   $13.40   $13.40  
  7 purchase totals = $682.34       $744.9086   $744.91   $744.95   $744.90