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 $116.54   11.582%   $130.0377   $130.04   $130.05   $130.00  
  Purchase #2 $172.81   10.274%   $190.5645   $190.56   $190.55   $190.60  
  Purchase #3 $144.59   9.231%   $157.9371   $157.94   $157.95   $157.90  
  Purchase #4 $58.54   12.220%   $65.6936   $65.69   $65.70   $65.70  
  Purchase #5 $102.25   12.864%   $115.4034   $115.40   $115.40   $115.40  
  Purchase #6 $114.36   12.136%   $128.2387   $128.24   $128.25   $128.20  
  Purchase #7 $210.32   7.856%   $226.8427   $226.84   $226.85   $226.80  
  7 purchase totals = $919.41       $1,014.7177   $1,014.71   $1,014.75   $1,014.60