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 $224.45   12.721%   $253.0023   $253.00   $253.00   $253.00  
  Purchase #2 $106.78   11.286%   $118.8312   $118.83   $118.85   $118.80  
  Purchase #3 $192.75   10.703%   $213.38   $213.38   $213.40   $213.40  
  Purchase #4 $103.47   10.413%   $114.2443   $114.24   $114.25   $114.20  
  Purchase #5 $208.25   9.319%   $227.6568   $227.66   $227.65   $227.70  
  Purchase #6 $46.94   9.393%   $51.3491   $51.35   $51.35   $51.30  
  Purchase #7 $108.85   5.287%   $114.6049   $114.60   $114.60   $114.60  
  7 purchase totals = $991.49       $1,093.0686   $1,093.06   $1,093.10   $1,093.00