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	$250.49	11.836%	$280.138	$280.14	$280.15	$280.10
Purchase #2	$9.29	9.784%	$10.1989	$10.20	$10.20	$10.20
Purchase #3	$208.83	6.752%	$222.9302	$222.93	$222.95	$222.90
Purchase #4	$158.69	8.748%	$172.5722	$172.57	$172.55	$172.60
Purchase #5	$22.67	6.844%	$24.2215	$24.22	$24.20	$24.20
Purchase #6	$222.99	11.284%	$248.1522	$248.15	$248.15	$248.20
Purchase #7	$130.82	6.639%	$139.5051	$139.51	$139.50	$139.50
7 purchase totals =	$1,003.78		$1,097.7181	$1,097.72	$1,097.70	$1,097.70