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 $208.66   6.373%   $221.9579   $221.96   $221.95   $222.00  
  Purchase #2 $60.41   4.551%   $63.1593   $63.16   $63.15   $63.20  
  Purchase #3 $203.27   10.789%   $225.2008   $225.20   $225.20   $225.20  
  Purchase #4 $209.45   3.609%   $217.0091   $217.01   $217.00   $217.00  
  Purchase #5 $68.54   3.574%   $70.9896   $70.99   $71.00   $71.00  
  Purchase #6 $216.44   13.156%   $244.9148   $244.91   $244.90   $244.90  
  Purchase #7 $50.69   10.728%   $56.128   $56.13   $56.15   $56.10  
  7 purchase totals = $1,017.46       $1,099.3595   $1,099.36   $1,099.35   $1,099.40