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 $192.63   12.726%   $217.1441   $217.14   $217.15   $217.10  
  Purchase #2 $44.91   3.434%   $46.4522   $46.45   $46.45   $46.50  
  Purchase #3 $49.44   6.244%   $52.527   $52.53   $52.55   $52.50  
  Purchase #4 $168.93   4.721%   $176.9052   $176.91   $176.90   $176.90  
  Purchase #5 $209.76   11.856%   $234.6291   $234.63   $234.65   $234.60  
  Purchase #6 $83.61   5.637%   $88.3231   $88.32   $88.30   $88.30  
  Purchase #7 $211.90   7.151%   $227.053   $227.05   $227.05   $227.10  
  7 purchase totals = $961.18       $1,043.0337   $1,043.03   $1,043.05   $1,043.00