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	$26.85	11.874%	$30.0382	$30.04	$30.05	$30.00
Purchase #2	$109.64	4.656%	$114.7448	$114.74	$114.75	$114.70
Purchase #3	$56.78	4.874%	$59.5475	$59.55	$59.55	$59.50
Purchase #4	$77.66	11.584%	$86.6561	$86.66	$86.65	$86.70
Purchase #5	$80.50	11.735%	$89.9467	$89.95	$89.95	$89.90
Purchase #6	$17.85	5.524%	$18.836	$18.84	$18.85	$18.80
Purchase #7	$38.50	6.273%	$40.9151	$40.92	$40.90	$40.90
7 purchase totals =	$407.78		$440.6844	$440.70	$440.70	$440.50