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 $47.72   10.227%   $52.6003   $52.60   $52.60   $52.60  
  Purchase #2 $233.59   3.267%   $241.2214   $241.22   $241.20   $241.20  
  Purchase #3 $236.63   7.580%   $254.5666   $254.57   $254.55   $254.60  
  Purchase #4 $48.91   5.677%   $51.6866   $51.69   $51.70   $51.70  
  Purchase #5 $128.72   4.174%   $134.0928   $134.09   $134.10   $134.10  
  Purchase #6 $77.39   10.758%   $85.7156   $85.72   $85.70   $85.70  
  Purchase #7 $198.94   4.581%   $208.0534   $208.05   $208.05   $208.10  
  7 purchase totals = $971.90       $1,027.9367   $1,027.94   $1,027.90   $1,028.00