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	$47.94	13.540%	$54.4311	$54.43	$54.45	$54.40
Purchase #2	$105.67	6.338%	$112.3674	$112.37	$112.35	$112.40
Purchase #3	$73.25	12.249%	$82.2224	$82.22	$82.20	$82.20
Purchase #4	$100.81	4.871%	$105.7205	$105.72	$105.70	$105.70
Purchase #5	$200.69	3.188%	$207.088	$207.09	$207.10	$207.10
Purchase #6	$82.76	6.359%	$88.0227	$88.02	$88.00	$88.00
Purchase #7	$36.84	9.373%	$40.293	$40.29	$40.30	$40.30
7 purchase totals =	$647.96		$690.1451	$690.14	$690.10	$690.10