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 $185.76   13.334%   $210.5292   $210.53   $210.55   $210.50  
  Purchase #2 $226.51   13.865%   $257.9156   $257.92   $257.90   $257.90  
  Purchase #3 $90.33   7.432%   $97.0433   $97.04   $97.05   $97.00  
  Purchase #4 $36.90   11.832%   $41.266   $41.27   $41.25   $41.30  
  Purchase #5 $162.98   13.794%   $185.4615   $185.46   $185.45   $185.50  
  Purchase #6 $156.48   12.845%   $176.5799   $176.58   $176.60   $176.60  
  Purchase #7 $185.57   4.493%   $193.9077   $193.91   $193.90   $193.90  
  7 purchase totals = $1,044.53       $1,162.7032   $1,162.71   $1,162.70   $1,162.70