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 $66.85   9.717%   $73.3458   $73.35   $73.35   $73.30  
  Purchase #2 $22.76   4.819%   $23.8568   $23.86   $23.85   $23.90  
  Purchase #3 $120.25   3.541%   $124.5081   $124.51   $124.50   $124.50  
  Purchase #4 $32.66   5.587%   $34.4847   $34.48   $34.50   $34.50  
  Purchase #5 $54.88   4.612%   $57.4111   $57.41   $57.40   $57.40  
  Purchase #6 $199.96   4.358%   $208.6743   $208.67   $208.65   $208.70  
  Purchase #7 $178.58   4.211%   $186.1   $186.10   $186.10   $186.10  
  7 purchase totals = $675.94       $708.3808   $708.38   $708.35   $708.40