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	$25.52	10.308%	$28.1506	$28.15	$28.15	$28.20
Purchase #2	$86.59	11.286%	$96.3625	$96.36	$96.35	$96.40
Purchase #3	$68.86	4.727%	$72.115	$72.12	$72.10	$72.10
Purchase #4	$51.49	5.793%	$54.4728	$54.47	$54.45	$54.50
Purchase #5	$207.41	8.242%	$224.5047	$224.50	$224.50	$224.50
Purchase #6	$115.83	13.630%	$131.6176	$131.62	$131.60	$131.60
Purchase #7	$14.40	10.114%	$15.8564	$15.86	$15.85	$15.90
7 purchase totals =	$570.10		$623.0796	$623.08	$623.00	$623.20