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 $65.79   11.346%   $73.2545   $73.25   $73.25   $73.30  
  Purchase #2 $219.52   9.135%   $239.5732   $239.57   $239.55   $239.60  
  Purchase #3 $142.71   7.687%   $153.6801   $153.68   $153.70   $153.70  
  Purchase #4 $208.42   9.127%   $227.4425   $227.44   $227.45   $227.40  
  Purchase #5 $71.75   7.156%   $76.8844   $76.88   $76.90   $76.90  
  Purchase #6 $234.41   7.762%   $252.6049   $252.60   $252.60   $252.60  
  Purchase #7 $229.76   13.404%   $260.557   $260.56   $260.55   $260.60  
  7 purchase totals = $1,172.36       $1,283.9966   $1,283.98   $1,284.00   $1,284.10