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 $55.45   7.262%   $59.4768   $59.48   $59.50   $59.50  
  Purchase #2 $228.83   8.395%   $248.0403   $248.04   $248.05   $248.00  
  Purchase #3 $88.54   10.152%   $97.5286   $97.53   $97.55   $97.50  
  Purchase #4 $244.86   11.586%   $273.2295   $273.23   $273.25   $273.20  
  Purchase #5 $182.57   12.423%   $205.2507   $205.25   $205.25   $205.30  
  Purchase #6 $207.27   3.247%   $214.0001   $214.00   $214.00   $214.00  
  Purchase #7 $168.80   3.523%   $174.7468   $174.75   $174.75   $174.70  
  7 purchase totals = $1,176.32       $1,272.2728   $1,272.28   $1,272.35   $1,272.20