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 $246.99   5.109%   $259.6087   $259.61   $259.60   $259.60  
  Purchase #2 $132.29   11.423%   $147.4015   $147.40   $147.40   $147.40  
  Purchase #3 $234.32   4.401%   $244.6324   $244.63   $244.65   $244.60  
  Purchase #4 $241.28   12.684%   $271.884   $271.88   $271.90   $271.90  
  Purchase #5 $119.51   11.491%   $133.2429   $133.24   $133.25   $133.20  
  Purchase #6 $162.99   12.741%   $183.7566   $183.76   $183.75   $183.80  
  Purchase #7 $74.25   11.286%   $82.6299   $82.63   $82.65   $82.60  
  7 purchase totals = $1,211.63       $1,323.1560   $1,323.15   $1,323.20   $1,323.10