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 $236.83   13.872%   $269.6831   $269.68   $269.70   $269.70  
  Purchase #2 $60.92   4.582%   $63.7114   $63.71   $63.70   $63.70  
  Purchase #3 $168.56   11.167%   $187.3831   $187.38   $187.40   $187.40  
  Purchase #4 $82.74   13.107%   $93.5847   $93.58   $93.60   $93.60  
  Purchase #5 $12.99   3.565%   $13.4531   $13.45   $13.45   $13.50  
  Purchase #6 $62.63   11.416%   $69.7798   $69.78   $69.80   $69.80  
  Purchase #7 $62.32   5.778%   $65.9208   $65.92   $65.90   $65.90  
  7 purchase totals = $686.99       $763.5160   $763.50   $763.55   $763.60