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 $60.39   4.236%   $62.9481   $62.95   $62.95   $62.90  
  Purchase #2 $78.68   13.211%   $89.0744   $89.07   $89.05   $89.10  
  Purchase #3 $176.56   4.147%   $183.8819   $183.88   $183.90   $183.90  
  Purchase #4 $79.25   4.840%   $83.0857   $83.09   $83.10   $83.10  
  Purchase #5 $116.43   7.212%   $124.8269   $124.83   $124.85   $124.80  
  Purchase #6 $226.88   4.242%   $236.5042   $236.50   $236.50   $236.50  
  Purchase #7 $13.50   11.426%   $15.0425   $15.04   $15.05   $15.00  
  7 purchase totals = $751.69       $795.3637   $795.36   $795.40   $795.30