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 $211.83   12.138%   $237.5419   $237.54   $237.55   $237.50  
  Purchase #2 $13.26   4.208%   $13.818   $13.82   $13.80   $13.80  
  Purchase #3 $19.47   12.391%   $21.8825   $21.88   $21.90   $21.90  
  Purchase #4 $64.45   10.295%   $71.0851   $71.09   $71.10   $71.10  
  Purchase #5 $176.54   5.126%   $185.5894   $185.59   $185.60   $185.60  
  Purchase #6 $21.26   9.810%   $23.3456   $23.35   $23.35   $23.30  
  Purchase #7 $164.50   11.493%   $183.406   $183.41   $183.40   $183.40  
  7 purchase totals = $671.31       $736.6685   $736.68   $736.70   $736.60