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 $61.66   3.712%   $63.9488   $63.95   $63.95   $63.90  
  Purchase #2 $36.47   12.492%   $41.0258   $41.03   $41.05   $41.00  
  Purchase #3 $163.36   6.299%   $173.65   $173.65   $173.65   $173.70  
  Purchase #4 $73.67   10.563%   $81.4518   $81.45   $81.45   $81.50  
  Purchase #5 $89.57   10.804%   $99.2471   $99.25   $99.25   $99.20  
  Purchase #6 $130.41   3.282%   $134.6901   $134.69   $134.70   $134.70  
  Purchase #7 $90.79   8.182%   $98.2184   $98.22   $98.20   $98.20  
  7 purchase totals = $645.93       $692.2320   $692.24   $692.25   $692.20