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	$166.30	13.419%	$188.6158	$188.62	$188.60	$188.60
Purchase #2	$152.72	13.844%	$173.8626	$173.86	$173.85	$173.90
Purchase #3	$42.51	5.850%	$44.9968	$45.00	$45.00	$45.00
Purchase #4	$21.46	5.739%	$22.6916	$22.69	$22.70	$22.70
Purchase #5	$77.48	7.694%	$83.4413	$83.44	$83.45	$83.40
Purchase #6	$14.44	3.476%	$14.9419	$14.94	$14.95	$14.90
Purchase #7	$148.58	6.731%	$158.5809	$158.58	$158.60	$158.60
7 purchase totals =	$623.49		$687.1309	$687.13	$687.15	$687.10