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 $191.71   8.673%   $208.337   $208.34   $208.35   $208.30  
  Purchase #2 $35.92   6.366%   $38.2067   $38.21   $38.20   $38.20  
  Purchase #3 $180.54   7.151%   $193.4504   $193.45   $193.45   $193.50  
  Purchase #4 $86.97   10.840%   $96.3975   $96.40   $96.40   $96.40  
  Purchase #5 $235.48   5.699%   $248.9   $248.90   $248.90   $248.90  
  Purchase #6 $238.71   11.560%   $266.3049   $266.30   $266.30   $266.30  
  Purchase #7 $186.28   10.190%   $205.2619   $205.26   $205.25   $205.30  
  7 purchase totals = $1,155.61       $1,256.8584   $1,256.86   $1,256.85   $1,256.90