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 $58.36   8.466%   $63.3008   $63.30   $63.30   $63.30  
  Purchase #2 $35.30   7.327%   $37.8864   $37.89   $37.90   $37.90  
  Purchase #3 $47.46   3.719%   $49.225   $49.23   $49.25   $49.20  
  Purchase #4 $208.77   11.185%   $232.1209   $232.12   $232.10   $232.10  
  Purchase #5 $178.69   12.255%   $200.5885   $200.59   $200.60   $200.60  
  Purchase #6 $42.77   11.664%   $47.7587   $47.76   $47.75   $47.80  
  Purchase #7 $241.50   11.271%   $268.7195   $268.72   $268.70   $268.70  
  7 purchase totals = $812.85       $899.5998   $899.61   $899.60   $899.60