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	$226.77	12.764%	$255.7149	$255.71	$255.70	$255.70
Purchase #2	$225.31	5.747%	$238.2586	$238.26	$238.25	$238.30
Purchase #3	$217.61	9.351%	$237.9587	$237.96	$237.95	$238.00
Purchase #4	$169.97	5.406%	$179.1586	$179.16	$179.15	$179.20
Purchase #5	$40.41	4.186%	$42.1016	$42.10	$42.10	$42.10
Purchase #6	$175.99	10.523%	$194.5094	$194.51	$194.50	$194.50
Purchase #7	$222.33	13.219%	$251.7198	$251.72	$251.70	$251.70
7 purchase totals =	$1,278.39		$1,399.4216	$1,399.42	$1,399.35	$1,399.50