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	$241.81	7.275%	$259.4017	$259.40	$259.40	$259.40
Purchase #2	$216.98	3.754%	$225.1254	$225.13	$225.15	$225.10
Purchase #3	$104.51	10.395%	$115.3738	$115.37	$115.35	$115.40
Purchase #4	$212.71	4.494%	$222.2692	$222.27	$222.25	$222.30
Purchase #5	$203.25	4.169%	$211.7235	$211.72	$211.70	$211.70
Purchase #6	$178.99	9.760%	$196.4594	$196.46	$196.45	$196.50
Purchase #7	$71.52	8.456%	$77.5677	$77.57	$77.55	$77.60
7 purchase totals =	$1,229.77		$1,307.9207	$1,307.92	$1,307.85	$1,308.00