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 $9.56   4.212%   $9.9627   $9.96   $9.95   $10.00  
  Purchase #2 $79.58   13.128%   $90.0273   $90.03   $90.05   $90.00  
  Purchase #3 $206.40   7.777%   $222.4517   $222.45   $222.45   $222.50  
  Purchase #4 $242.34   12.201%   $271.9079   $271.91   $271.90   $271.90  
  Purchase #5 $94.69   3.345%   $97.8574   $97.86   $97.85   $97.90  
  Purchase #6 $136.36   4.623%   $142.6639   $142.66   $142.65   $142.70  
  Purchase #7 $49.93   4.524%   $52.1888   $52.19   $52.20   $52.20  
  7 purchase totals = $818.86       $887.0597   $887.06   $887.05   $887.20