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	$246.32	13.686%	$280.0314	$280.03	$280.05	$280.00
Purchase #2	$19.86	6.492%	$21.1493	$21.15	$21.15	$21.10
Purchase #3	$161.76	10.834%	$179.2851	$179.29	$179.30	$179.30
Purchase #4	$38.71	12.754%	$43.6471	$43.65	$43.65	$43.60
Purchase #5	$156.75	10.694%	$173.5128	$173.51	$173.50	$173.50
Purchase #6	$229.79	10.570%	$254.0788	$254.08	$254.10	$254.10
Purchase #7	$106.88	11.760%	$119.4491	$119.45	$119.45	$119.40
7 purchase totals =	$960.07		$1,071.1536	$1,071.16	$1,071.20	$1,071.00