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 $246.54   8.808%   $268.2552   $268.26   $268.25   $268.30  
  Purchase #2 $11.33   5.784%   $11.9853   $11.99   $12.00   $12.00  
  Purchase #3 $180.94   7.509%   $194.5268   $194.53   $194.55   $194.50  
  Purchase #4 $144.47   8.146%   $156.2385   $156.24   $156.25   $156.20  
  Purchase #5 $207.69   7.262%   $222.7724   $222.77   $222.75   $222.80  
  Purchase #6 $163.67   9.771%   $179.6622   $179.66   $179.65   $179.70  
  Purchase #7 $174.26   9.491%   $190.799   $190.80   $190.80   $190.80  
  7 purchase totals = $1,128.90       $1,224.2394   $1,224.25   $1,224.25   $1,224.30