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 $238.99   12.353%   $268.5124   $268.51   $268.50   $268.50  
  Purchase #2 $141.61   11.219%   $157.4972   $157.50   $157.50   $157.50  
  Purchase #3 $142.33   6.443%   $151.5003   $151.50   $151.50   $151.50  
  Purchase #4 $36.98   4.795%   $38.7532   $38.75   $38.75   $38.80  
  Purchase #5 $248.27   7.212%   $266.1752   $266.18   $266.20   $266.20  
  Purchase #6 $29.36   13.225%   $33.2429   $33.24   $33.25   $33.20  
  Purchase #7 $93.39   5.580%   $98.6012   $98.60   $98.60   $98.60  
  7 purchase totals = $930.93       $1,014.2824   $1,014.28   $1,014.30   $1,014.30