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 $107.81   10.545%   $119.1786   $119.18   $119.20   $119.20  
  Purchase #2 $227.74   6.115%   $241.6663   $241.67   $241.65   $241.70  
  Purchase #3 $32.67   9.437%   $35.7531   $35.75   $35.75   $35.80  
  Purchase #4 $215.33   10.542%   $238.0301   $238.03   $238.05   $238.00  
  Purchase #5 $181.62   8.168%   $196.4547   $196.45   $196.45   $196.50  
  Purchase #6 $227.27   13.331%   $257.5674   $257.57   $257.55   $257.60  
  Purchase #7 $183.30   13.689%   $208.3919   $208.39   $208.40   $208.40  
  7 purchase totals = $1,175.74       $1,297.0421   $1,297.04   $1,297.05   $1,297.20