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	$70.87	12.199%	$79.5154	$79.52	$79.50	$79.50
Purchase #2	$109.34	4.561%	$114.327	$114.33	$114.35	$114.30
Purchase #3	$224.86	12.580%	$253.1474	$253.15	$253.15	$253.10
Purchase #4	$52.58	10.357%	$58.0257	$58.03	$58.05	$58.00
Purchase #5	$85.31	5.202%	$89.7478	$89.75	$89.75	$89.70
Purchase #6	$18.29	8.601%	$19.8631	$19.86	$19.85	$19.90
Purchase #7	$126.46	12.261%	$141.9653	$141.97	$141.95	$142.00
7 purchase totals =	$687.71		$756.5917	$756.61	$756.60	$756.50