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 $60.43   5.624%   $63.8286   $63.83   $63.85   $63.80  
  Purchase #2 $216.95   10.239%   $239.1635   $239.16   $239.15   $239.20  
  Purchase #3 $203.44   8.801%   $221.3448   $221.34   $221.35   $221.30  
  Purchase #4 $6.70   12.402%   $7.5309   $7.53   $7.55   $7.50  
  Purchase #5 $243.77   6.419%   $259.4176   $259.42   $259.40   $259.40  
  Purchase #6 $85.75   8.725%   $93.2317   $93.23   $93.25   $93.20  
  Purchase #7 $171.71   10.680%   $190.0486   $190.05   $190.05   $190.00  
  7 purchase totals = $988.75       $1,074.5657   $1,074.56   $1,074.60   $1,074.40