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	$19.63	4.649%	$20.5426	$20.54	$20.55	$20.50
Purchase #2	$67.71	8.445%	$73.4281	$73.43	$73.45	$73.40
Purchase #3	$109.78	12.783%	$123.8132	$123.81	$123.80	$123.80
Purchase #4	$94.81	8.157%	$102.5437	$102.54	$102.55	$102.50
Purchase #5	$13.33	11.571%	$14.8724	$14.87	$14.85	$14.90
Purchase #6	$51.95	9.321%	$56.7923	$56.79	$56.80	$56.80
Purchase #7	$121.91	4.649%	$127.5776	$127.58	$127.60	$127.60
7 purchase totals =	$479.12		$519.5699	$519.56	$519.60	$519.50