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 $105.82   8.263%   $114.5639   $114.56   $114.55   $114.60  
  Purchase #2 $24.83   10.129%   $27.345   $27.35   $27.35   $27.30  
  Purchase #3 $19.82   7.783%   $21.3626   $21.36   $21.35   $21.40  
  Purchase #4 $242.58   7.115%   $259.8396   $259.84   $259.85   $259.80  
  Purchase #5 $123.29   4.394%   $128.7074   $128.71   $128.70   $128.70  
  Purchase #6 $202.73   5.757%   $214.4012   $214.40   $214.40   $214.40  
  Purchase #7 $40.81   13.712%   $46.4059   $46.41   $46.40   $46.40  
  7 purchase totals = $759.88       $812.6256   $812.63   $812.60   $812.60