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 $60.38   10.111%   $66.485   $66.49   $66.50   $66.50  
  Purchase #2 $226.84   5.304%   $238.8716   $238.87   $238.85   $238.90  
  Purchase #3 $56.46   3.663%   $58.5281   $58.53   $58.55   $58.50  
  Purchase #4 $186.40   11.790%   $208.3766   $208.38   $208.40   $208.40  
  Purchase #5 $50.46   12.521%   $56.7781   $56.78   $56.80   $56.80  
  Purchase #6 $126.48   5.190%   $133.0443   $133.04   $133.05   $133.00  
  Purchase #7 $9.62   8.803%   $10.4668   $10.47   $10.45   $10.50  
  7 purchase totals = $716.64       $772.5505   $772.56   $772.60   $772.60