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 $238.32   8.861%   $259.4375   $259.44   $259.45   $259.40  
  Purchase #2 $13.45   9.184%   $14.6852   $14.69   $14.70   $14.70  
  Purchase #3 $153.87   11.541%   $171.6281   $171.63   $171.65   $171.60  
  Purchase #4 $205.99   6.131%   $218.6192   $218.62   $218.60   $218.60  
  Purchase #5 $242.25   3.179%   $249.9511   $249.95   $249.95   $250.00  
  Purchase #6 $148.43   9.143%   $162.001   $162.00   $162.00   $162.00  
  Purchase #7 $159.60   11.570%   $178.0657   $178.07   $178.05   $178.10  
  7 purchase totals = $1,161.91       $1,254.3878   $1,254.40   $1,254.40   $1,254.40