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 $235.35   11.122%   $261.5256   $261.53   $261.55   $261.50  
  Purchase #2 $12.43   6.864%   $13.2832   $13.28   $13.30   $13.30  
  Purchase #3 $183.83   5.131%   $193.2623   $193.26   $193.25   $193.30  
  Purchase #4 $105.70   6.837%   $112.9267   $112.93   $112.95   $112.90  
  Purchase #5 $147.50   11.180%   $163.9905   $163.99   $164.00   $164.00  
  Purchase #6 $136.44   11.194%   $151.7131   $151.71   $151.70   $151.70  
  Purchase #7 $183.43   13.281%   $207.7913   $207.79   $207.80   $207.80  
  7 purchase totals = $1,004.68       $1,104.4927   $1,104.49   $1,104.55   $1,104.50