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 $54.49   10.849%   $60.4016   $60.40   $60.40   $60.40  
  Purchase #2 $200.49   7.721%   $215.9698   $215.97   $215.95   $216.00  
  Purchase #3 $90.81   8.509%   $98.537   $98.54   $98.55   $98.50  
  Purchase #4 $208.59   3.849%   $216.6186   $216.62   $216.60   $216.60  
  Purchase #5 $66.27   5.410%   $69.8552   $69.86   $69.85   $69.90  
  Purchase #6 $187.91   10.327%   $207.3155   $207.32   $207.30   $207.30  
  Purchase #7 $64.30   8.667%   $69.8729   $69.87   $69.85   $69.90  
  7 purchase totals = $872.86       $938.5706   $938.58   $938.50   $938.60