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 $230.83   13.616%   $262.2598   $262.26   $262.25   $262.30  
  Purchase #2 $209.57   9.786%   $230.0785   $230.08   $230.10   $230.10  
  Purchase #3 $105.70   6.377%   $112.4405   $112.44   $112.45   $112.40  
  Purchase #4 $147.86   5.151%   $155.4763   $155.48   $155.50   $155.50  
  Purchase #5 $182.42   10.380%   $201.3552   $201.36   $201.35   $201.40  
  Purchase #6 $239.61   12.578%   $269.7481   $269.75   $269.75   $269.70  
  Purchase #7 $35.91   5.174%   $37.768   $37.77   $37.75   $37.80  
  7 purchase totals = $1,151.90       $1,269.1264   $1,269.14   $1,269.15   $1,269.20