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	$16.94	10.200%	$18.6679	$18.67	$18.65	$18.70
Purchase #2	$215.94	4.637%	$225.9531	$225.95	$225.95	$226.00
Purchase #3	$82.53	8.184%	$89.2843	$89.28	$89.30	$89.30
Purchase #4	$50.40	10.779%	$55.8326	$55.83	$55.85	$55.80
Purchase #5	$51.79	4.438%	$54.0884	$54.09	$54.10	$54.10
Purchase #6	$111.65	5.150%	$117.4	$117.40	$117.40	$117.40
Purchase #7	$77.92	6.152%	$82.7136	$82.71	$82.70	$82.70
7 purchase totals =	$607.17		$643.9399	$643.93	$643.95	$644.00