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 $60.39   7.708%   $65.0449   $65.04   $65.05   $65.00  
  Purchase #2 $221.87   8.452%   $240.6225   $240.62   $240.60   $240.60  
  Purchase #3 $208.66   6.139%   $221.4696   $221.47   $221.45   $221.50  
  Purchase #4 $156.77   5.206%   $164.9314   $164.93   $164.95   $164.90  
  Purchase #5 $66.76   3.830%   $69.3169   $69.32   $69.30   $69.30  
  Purchase #6 $63.47   3.530%   $65.7105   $65.71   $65.70   $65.70  
  Purchase #7 $83.32   10.360%   $91.952   $91.95   $91.95   $92.00  
  7 purchase totals = $861.24       $919.0478   $919.04   $919.00   $919.00