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	$247.27	12.678%	$278.6189	$278.62	$278.60	$278.60
Purchase #2	$53.91	10.186%	$59.4013	$59.40	$59.40	$59.40
Purchase #3	$207.86	13.381%	$235.6737	$235.67	$235.65	$235.70
Purchase #4	$174.88	9.167%	$190.9112	$190.91	$190.90	$190.90
Purchase #5	$73.82	4.686%	$77.2792	$77.28	$77.30	$77.30
Purchase #6	$9.89	5.162%	$10.4005	$10.40	$10.40	$10.40
Purchase #7	$236.62	6.355%	$251.6572	$251.66	$251.65	$251.70
7 purchase totals =	$1,004.25		$1,103.9420	$1,103.94	$1,103.90	$1,104.00