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	$65.74	6.701%	$70.1452	$70.15	$70.15	$70.10
Purchase #2	$88.84	10.308%	$97.9976	$98.00	$98.00	$98.00
Purchase #3	$8.41	9.752%	$9.2301	$9.23	$9.25	$9.20
Purchase #4	$47.26	12.768%	$53.2942	$53.29	$53.30	$53.30
Purchase #5	$59.41	5.188%	$62.4922	$62.49	$62.50	$62.50
Purchase #6	$90.37	10.200%	$99.5877	$99.59	$99.60	$99.60
Purchase #7	$238.88	12.753%	$269.3444	$269.34	$269.35	$269.30
7 purchase totals =	$598.91		$662.0914	$662.09	$662.15	$662.00