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 $127.57   6.835%   $136.2894   $136.29   $136.30   $136.30  
  Purchase #2 $224.67   5.422%   $236.8516   $236.85   $236.85   $236.90  
  Purchase #3 $43.45   3.135%   $44.8122   $44.81   $44.80   $44.80  
  Purchase #4 $205.43   4.510%   $214.6949   $214.69   $214.70   $214.70  
  Purchase #5 $79.77   12.630%   $89.845   $89.85   $89.85   $89.80  
  Purchase #6 $63.90   4.382%   $66.7001   $66.70   $66.70   $66.70  
  Purchase #7 $247.25   9.467%   $270.6572   $270.66   $270.65   $270.70  
  7 purchase totals = $992.04       $1,059.8504   $1,059.85   $1,059.85   $1,059.90