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	$182.37	4.262%	$190.1426	$190.14	$190.15	$190.10
Purchase #2	$102.52	13.329%	$116.1849	$116.18	$116.20	$116.20
Purchase #3	$149.83	11.800%	$167.5099	$167.51	$167.50	$167.50
Purchase #4	$86.58	4.287%	$90.2917	$90.29	$90.30	$90.30
Purchase #5	$195.35	7.541%	$210.0813	$210.08	$210.10	$210.10
Purchase #6	$11.84	7.195%	$12.6919	$12.69	$12.70	$12.70
Purchase #7	$50.74	6.575%	$54.0762	$54.08	$54.10	$54.10
7 purchase totals =	$779.23		$840.9785	$840.97	$841.05	$841.00