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	$153.64	8.306%	$166.4013	$166.40	$166.40	$166.40
Purchase #2	$246.55	12.247%	$276.745	$276.75	$276.75	$276.70
Purchase #3	$51.44	6.601%	$54.8356	$54.84	$54.85	$54.80
Purchase #4	$101.87	10.697%	$112.767	$112.77	$112.75	$112.80
Purchase #5	$180.94	8.486%	$196.2946	$196.29	$196.30	$196.30
Purchase #6	$98.28	4.856%	$103.0525	$103.05	$103.05	$103.10
Purchase #7	$110.76	11.693%	$123.7112	$123.71	$123.70	$123.70
7 purchase totals =	$943.48		$1,033.8072	$1,033.81	$1,033.80	$1,033.80