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	$80.62	11.233%	$89.676	$89.68	$89.70	$89.70
Purchase #2	$208.38	10.771%	$230.8246	$230.82	$230.80	$230.80
Purchase #3	$11.48	8.383%	$12.4424	$12.44	$12.45	$12.40
Purchase #4	$91.90	8.109%	$99.3522	$99.35	$99.35	$99.40
Purchase #5	$18.37	10.121%	$20.2292	$20.23	$20.25	$20.20
Purchase #6	$107.96	12.286%	$121.224	$121.22	$121.20	$121.20
Purchase #7	$39.52	9.813%	$43.3981	$43.40	$43.40	$43.40
7 purchase totals =	$558.23		$617.1465	$617.14	$617.15	$617.10