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 $60.64   5.426%   $63.9303   $63.93   $63.95   $63.90  
  Purchase #2 $248.55   3.358%   $256.8963   $256.90   $256.90   $256.90  
  Purchase #3 $206.73   11.774%   $231.0704   $231.07   $231.05   $231.10  
  Purchase #4 $123.62   8.338%   $133.9274   $133.93   $133.95   $133.90  
  Purchase #5 $75.29   13.509%   $85.4609   $85.46   $85.45   $85.50  
  Purchase #6 $232.51   9.348%   $254.245   $254.25   $254.25   $254.20  
  Purchase #7 $40.31   10.152%   $44.4023   $44.40   $44.40   $44.40  
  7 purchase totals = $987.65       $1,069.9326   $1,069.94   $1,069.95   $1,069.90