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 $236.28   13.868%   $269.0473   $269.05   $269.05   $269.00  
  Purchase #2 $190.55   12.572%   $214.5059   $214.51   $214.50   $214.50  
  Purchase #3 $118.59   7.595%   $127.5969   $127.60   $127.60   $127.60  
  Purchase #4 $180.95   6.435%   $192.5941   $192.59   $192.60   $192.60  
  Purchase #5 $163.57   4.812%   $171.441   $171.44   $171.45   $171.40  
  Purchase #6 $118.37   12.540%   $133.2136   $133.21   $133.20   $133.20  
  Purchase #7 $104.46   11.447%   $116.4175   $116.42   $116.40   $116.40  
  7 purchase totals = $1,112.77       $1,224.8163   $1,224.82   $1,224.80   $1,224.70