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	$228.33	5.140%	$240.0662	$240.07	$240.05	$240.10
Purchase #2	$174.63	12.267%	$196.0519	$196.05	$196.05	$196.10
Purchase #3	$160.45	4.615%	$167.8548	$167.85	$167.85	$167.90
Purchase #4	$232.29	11.287%	$258.5086	$258.51	$258.50	$258.50
Purchase #5	$188.57	9.131%	$205.7883	$205.79	$205.80	$205.80
Purchase #6	$153.88	12.768%	$173.5274	$173.53	$173.55	$173.50
Purchase #7	$141.25	3.242%	$145.8293	$145.83	$145.85	$145.80
7 purchase totals =	$1,279.40		$1,387.6265	$1,387.63	$1,387.65	$1,387.70