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 $108.81   6.866%   $116.2809   $116.28   $116.30   $116.30  
  Purchase #2 $224.57   13.313%   $254.467   $254.47   $254.45   $254.50  
  Purchase #3 $45.88   10.424%   $50.6625   $50.66   $50.65   $50.70  
  Purchase #4 $81.81   3.239%   $84.4598   $84.46   $84.45   $84.50  
  Purchase #5 $78.38   3.835%   $81.3859   $81.39   $81.40   $81.40  
  Purchase #6 $180.49   13.797%   $205.3922   $205.39   $205.40   $205.40  
  Purchase #7 $8.45   13.750%   $9.6119   $9.61   $9.60   $9.60  
  7 purchase totals = $728.39       $802.2602   $802.26   $802.25   $802.40