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 $102.42   11.262%   $113.9545   $113.95   $113.95   $114.00  
  Purchase #2 $234.94   6.404%   $249.9856   $249.99   $250.00   $250.00  
  Purchase #3 $244.28   7.600%   $262.8453   $262.85   $262.85   $262.80  
  Purchase #4 $216.69   11.572%   $241.7654   $241.77   $241.75   $241.80  
  Purchase #5 $222.89   5.145%   $234.3577   $234.36   $234.35   $234.40  
  Purchase #6 $201.83   12.369%   $226.7944   $226.79   $226.80   $226.80  
  Purchase #7 $239.25   12.527%   $269.2208   $269.22   $269.20   $269.20  
  7 purchase totals = $1,462.30       $1,598.9237   $1,598.93   $1,598.90   $1,599.00