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 $169.71   4.358%   $177.106   $177.11   $177.10   $177.10  
  Purchase #2 $226.32   6.848%   $241.8184   $241.82   $241.80   $241.80  
  Purchase #3 $248.89   5.104%   $261.5933   $261.59   $261.60   $261.60  
  Purchase #4 $83.79   10.234%   $92.3651   $92.37   $92.35   $92.40  
  Purchase #5 $131.83   7.474%   $141.683   $141.68   $141.70   $141.70  
  Purchase #6 $68.30   13.161%   $77.289   $77.29   $77.30   $77.30  
  Purchase #7 $247.83   12.229%   $278.1371   $278.14   $278.15   $278.10  
  7 purchase totals = $1,176.67       $1,269.9919   $1,270.00   $1,270.00   $1,270.00