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 $238.53   8.849%   $259.6375   $259.64   $259.65   $259.60  
  Purchase #2 $122.47   9.116%   $133.6344   $133.63   $133.65   $133.60  
  Purchase #3 $38.60   7.365%   $41.4429   $41.44   $41.45   $41.40  
  Purchase #4 $195.65   7.433%   $210.1927   $210.19   $210.20   $210.20  
  Purchase #5 $67.47   6.121%   $71.5998   $71.60   $71.60   $71.60  
  Purchase #6 $7.37   12.210%   $8.2699   $8.27   $8.25   $8.30  
  Purchase #7 $62.89   13.316%   $71.2644   $71.26   $71.25   $71.30  
  7 purchase totals = $732.98       $796.0416   $796.03   $796.05   $796.00