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 $242.87   8.542%   $263.616   $263.62   $263.60   $263.60  
  Purchase #2 $174.68   3.832%   $181.3737   $181.37   $181.35   $181.40  
  Purchase #3 $43.99   9.252%   $48.06   $48.06   $48.05   $48.10  
  Purchase #4 $218.79   3.535%   $226.5242   $226.52   $226.50   $226.50  
  Purchase #5 $49.63   11.512%   $55.3434   $55.34   $55.35   $55.30  
  Purchase #6 $27.27   10.509%   $30.1358   $30.14   $30.15   $30.10  
  Purchase #7 $114.26   3.368%   $118.1083   $118.11   $118.10   $118.10  
  7 purchase totals = $871.49       $923.1614   $923.16   $923.10   $923.10