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	$16.87	10.496%	$18.6407	$18.64	$18.65	$18.60
Purchase #2	$40.72	11.723%	$45.4936	$45.49	$45.50	$45.50
Purchase #3	$212.80	5.192%	$223.8486	$223.85	$223.85	$223.80
Purchase #4	$26.86	7.702%	$28.9288	$28.93	$28.95	$28.90
Purchase #5	$52.86	5.459%	$55.7456	$55.75	$55.75	$55.70
Purchase #6	$89.91	6.458%	$95.7164	$95.72	$95.70	$95.70
Purchase #7	$59.64	10.645%	$65.9887	$65.99	$66.00	$66.00
7 purchase totals =	$499.66		$534.3624	$534.37	$534.40	$534.20