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 $165.71   11.393%   $184.5893   $184.59   $184.60   $184.60  
  Purchase #2 $32.48   5.429%   $34.2433   $34.24   $34.25   $34.20  
  Purchase #3 $168.72   3.849%   $175.214   $175.21   $175.20   $175.20  
  Purchase #4 $228.83   4.532%   $239.2006   $239.20   $239.20   $239.20  
  Purchase #5 $250.81   6.860%   $268.0156   $268.02   $268.00   $268.00  
  Purchase #6 $68.91   11.866%   $77.0869   $77.09   $77.10   $77.10  
  Purchase #7 $34.73   12.565%   $39.0938   $39.09   $39.10   $39.10  
  7 purchase totals = $950.19       $1,017.4435   $1,017.44   $1,017.45   $1,017.40