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	$218.50	3.142%	$225.3653	$225.37	$225.35	$225.40
Purchase #2	$97.46	13.745%	$110.8559	$110.86	$110.85	$110.90
Purchase #3	$46.75	5.469%	$49.3068	$49.31	$49.30	$49.30
Purchase #4	$235.81	8.320%	$255.4294	$255.43	$255.45	$255.40
Purchase #5	$181.58	5.143%	$190.9187	$190.92	$190.90	$190.90
Purchase #6	$133.49	6.504%	$142.1722	$142.17	$142.15	$142.20
Purchase #7	$185.68	3.307%	$191.8204	$191.82	$191.80	$191.80
7 purchase totals =	$1,099.27		$1,165.8687	$1,165.88	$1,165.80	$1,165.90