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	$185.87	5.658%	$196.3865	$196.39	$196.40	$196.40
Purchase #2	$217.45	10.131%	$239.4799	$239.48	$239.50	$239.50
Purchase #3	$153.95	6.570%	$164.0645	$164.06	$164.05	$164.10
Purchase #4	$198.71	12.427%	$223.4037	$223.40	$223.40	$223.40
Purchase #5	$151.35	4.462%	$158.1032	$158.10	$158.10	$158.10
Purchase #6	$204.73	13.575%	$232.5221	$232.52	$232.50	$232.50
Purchase #7	$24.25	9.332%	$26.513	$26.51	$26.50	$26.50
7 purchase totals =	$1,136.31		$1,240.4729	$1,240.46	$1,240.45	$1,240.50