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	$207.95	13.849%	$236.749	$236.75	$236.75	$236.70
Purchase #2	$142.31	12.504%	$160.1044	$160.10	$160.10	$160.10
Purchase #3	$127.69	9.863%	$140.2841	$140.28	$140.30	$140.30
Purchase #4	$99.67	11.533%	$111.1649	$111.16	$111.15	$111.20
Purchase #5	$157.93	13.200%	$178.7768	$178.78	$178.80	$178.80
Purchase #6	$48.30	12.326%	$54.2535	$54.25	$54.25	$54.30
Purchase #7	$113.51	4.291%	$118.3807	$118.38	$118.40	$118.40
7 purchase totals =	$897.36		$999.7134	$999.70	$999.75	$999.80