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 $244.82   11.808%   $273.7283   $273.73   $273.75   $273.70  
  Purchase #2 $228.67   10.457%   $252.582   $252.58   $252.60   $252.60  
  Purchase #3 $244.92   10.762%   $271.2783   $271.28   $271.30   $271.30  
  Purchase #4 $221.40   8.873%   $241.0448   $241.04   $241.05   $241.00  
  Purchase #5 $84.92   12.414%   $95.462   $95.46   $95.45   $95.50  
  Purchase #6 $210.51   4.808%   $220.6313   $220.63   $220.65   $220.60  
  Purchase #7 $227.35   3.120%   $234.4433   $234.44   $234.45   $234.40  
  7 purchase totals = $1,462.59       $1,589.1700   $1,589.16   $1,589.25   $1,589.10