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	$16.61	13.675%	$18.8814	$18.88	$18.90	$18.90
Purchase #2	$123.69	10.172%	$136.2717	$136.27	$136.25	$136.30
Purchase #3	$228.35	12.574%	$257.0627	$257.06	$257.05	$257.10
Purchase #4	$54.95	6.868%	$58.724	$58.72	$58.70	$58.70
Purchase #5	$31.78	6.246%	$33.765	$33.77	$33.75	$33.80
Purchase #6	$151.75	11.459%	$169.139	$169.14	$169.15	$169.10
Purchase #7	$107.88	3.723%	$111.8964	$111.90	$111.90	$111.90
7 purchase totals =	$715.01		$785.7402	$785.74	$785.70	$785.80