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 $61.42   6.246%   $65.2563   $65.26   $65.25   $65.30  
  Purchase #2 $183.27   9.846%   $201.3148   $201.31   $201.30   $201.30  
  Purchase #3 $186.48   6.255%   $198.1443   $198.14   $198.15   $198.10  
  Purchase #4 $132.67   3.611%   $137.4607   $137.46   $137.45   $137.50  
  Purchase #5 $53.48   13.316%   $60.6014   $60.60   $60.60   $60.60  
  Purchase #6 $196.76   6.866%   $210.2695   $210.27   $210.25   $210.30  
  Purchase #7 $185.88   13.287%   $210.5779   $210.58   $210.60   $210.60  
  7 purchase totals = $999.96       $1,083.6249   $1,083.62   $1,083.60   $1,083.70