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 $130.68   11.762%   $146.0506   $146.05   $146.05   $146.10  
  Purchase #2 $71.48   4.374%   $74.6065   $74.61   $74.60   $74.60  
  Purchase #3 $74.84   10.850%   $82.9601   $82.96   $82.95   $83.00  
  Purchase #4 $241.73   4.342%   $252.2259   $252.23   $252.25   $252.20  
  Purchase #5 $98.84   5.677%   $104.4511   $104.45   $104.45   $104.50  
  Purchase #6 $191.55   11.671%   $213.9058   $213.91   $213.90   $213.90  
  Purchase #7 $136.29   9.321%   $148.9936   $148.99   $149.00   $149.00  
  7 purchase totals = $945.41       $1,023.1936   $1,023.20   $1,023.20   $1,023.30