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 $177.81   13.738%   $202.2375   $202.24   $202.25   $202.20  
  Purchase #2 $85.54   11.642%   $95.4986   $95.50   $95.50   $95.50  
  Purchase #3 $76.87   8.273%   $83.2295   $83.23   $83.25   $83.20  
  Purchase #4 $131.68   7.647%   $141.7496   $141.75   $141.75   $141.70  
  Purchase #5 $62.69   10.163%   $69.0612   $69.06   $69.05   $69.10  
  Purchase #6 $123.99   5.136%   $130.3581   $130.36   $130.35   $130.40  
  Purchase #7 $104.99   13.414%   $119.0734   $119.07   $119.05   $119.10  
  7 purchase totals = $763.57       $841.2079   $841.21   $841.20   $841.20