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 $242.95   4.194%   $253.1393   $253.14   $253.15   $253.10  
  Purchase #2 $170.28   9.660%   $186.729   $186.73   $186.75   $186.70  
  Purchase #3 $155.92   4.341%   $162.6885   $162.69   $162.70   $162.70  
  Purchase #4 $73.56   8.453%   $79.778   $79.78   $79.80   $79.80  
  Purchase #5 $192.28   11.654%   $214.6883   $214.69   $214.70   $214.70  
  Purchase #6 $35.81   6.152%   $38.013   $38.01   $38.00   $38.00  
  Purchase #7 $248.81   8.788%   $270.6754   $270.68   $270.70   $270.70  
  7 purchase totals = $1,119.61       $1,205.7115   $1,205.72   $1,205.80   $1,205.70