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 $87.39   11.724%   $97.6356   $97.64   $97.65   $97.60  
  Purchase #2 $5.84   12.855%   $6.5907   $6.59   $6.60   $6.60  
  Purchase #3 $188.81   5.794%   $199.7497   $199.75   $199.75   $199.70  
  Purchase #4 $188.42   11.464%   $210.0205   $210.02   $210.00   $210.00  
  Purchase #5 $118.64   6.620%   $126.494   $126.49   $126.50   $126.50  
  Purchase #6 $95.38   3.748%   $98.9548   $98.95   $98.95   $99.00  
  Purchase #7 $208.76   9.729%   $229.0703   $229.07   $229.05   $229.10  
  7 purchase totals = $893.24       $968.5156   $968.51   $968.50   $968.50