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 $223.88   10.157%   $246.6195   $246.62   $246.60   $246.60  
  Purchase #2 $70.60   9.128%   $77.0444   $77.04   $77.05   $77.00  
  Purchase #3 $53.54   7.271%   $57.4329   $57.43   $57.45   $57.40  
  Purchase #4 $103.87   10.410%   $114.6829   $114.68   $114.70   $114.70  
  Purchase #5 $236.50   11.275%   $263.1654   $263.17   $263.15   $263.20  
  Purchase #6 $234.45   7.638%   $252.3573   $252.36   $252.35   $252.40  
  Purchase #7 $242.44   3.440%   $250.7799   $250.78   $250.80   $250.80  
  7 purchase totals = $1,165.28       $1,262.0823   $1,262.08   $1,262.10   $1,262.10