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	$77.77	3.429%	$80.4367	$80.44	$80.45	$80.40
Purchase #2	$135.77	6.440%	$144.5136	$144.51	$144.50	$144.50
Purchase #3	$200.38	7.652%	$215.7131	$215.71	$215.70	$215.70
Purchase #4	$112.47	5.649%	$118.8234	$118.82	$118.80	$118.80
Purchase #5	$142.87	10.602%	$158.0171	$158.02	$158.00	$158.00
Purchase #6	$190.94	4.114%	$198.7953	$198.80	$198.80	$198.80
Purchase #7	$49.25	8.458%	$53.4156	$53.42	$53.40	$53.40
7 purchase totals =	$909.45		$969.7148	$969.72	$969.65	$969.60