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	$9.72	5.429%	$10.2477	$10.25	$10.25	$10.20
Purchase #2	$122.96	6.233%	$130.6241	$130.62	$130.60	$130.60
Purchase #3	$143.92	6.791%	$153.6936	$153.69	$153.70	$153.70
Purchase #4	$122.64	13.681%	$139.4184	$139.42	$139.40	$139.40
Purchase #5	$136.99	4.545%	$143.2162	$143.22	$143.20	$143.20
Purchase #6	$65.37	7.810%	$70.4754	$70.48	$70.50	$70.50
Purchase #7	$17.94	13.157%	$20.3004	$20.30	$20.30	$20.30
7 purchase totals =	$619.54		$667.9758	$667.98	$667.95	$667.90