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 $41.69   7.176%   $44.6817   $44.68   $44.70   $44.70  
  Purchase #2 $101.48   13.234%   $114.9099   $114.91   $114.90   $114.90  
  Purchase #3 $185.37   5.510%   $195.5839   $195.58   $195.60   $195.60  
  Purchase #4 $66.66   13.161%   $75.4331   $75.43   $75.45   $75.40  
  Purchase #5 $50.27   11.618%   $56.1104   $56.11   $56.10   $56.10  
  Purchase #6 $24.92   12.754%   $28.0983   $28.10   $28.10   $28.10  
  Purchase #7 $38.63   4.758%   $40.468   $40.47   $40.45   $40.50  
  7 purchase totals = $509.02       $555.2853   $555.28   $555.30   $555.30