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 $40.28   8.206%   $43.5854   $43.59   $43.60   $43.60  
  Purchase #2 $111.58   6.135%   $118.4254   $118.43   $118.45   $118.40  
  Purchase #3 $104.35   10.870%   $115.6928   $115.69   $115.70   $115.70  
  Purchase #4 $185.79   11.315%   $206.8121   $206.81   $206.80   $206.80  
  Purchase #5 $220.62   13.226%   $249.7992   $249.80   $249.80   $249.80  
  Purchase #6 $172.75   10.710%   $191.2515   $191.25   $191.25   $191.30  
  Purchase #7 $24.32   8.353%   $26.3514   $26.35   $26.35   $26.40  
  7 purchase totals = $859.69       $951.9178   $951.92   $951.95   $952.00