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	$202.95	11.146%	$225.5708	$225.57	$225.55	$225.60
Purchase #2	$173.25	9.144%	$189.092	$189.09	$189.10	$189.10
Purchase #3	$93.35	11.828%	$104.3914	$104.39	$104.40	$104.40
Purchase #4	$228.26	5.750%	$241.385	$241.39	$241.40	$241.40
Purchase #5	$225.89	13.244%	$255.8069	$255.81	$255.80	$255.80
Purchase #6	$127.26	4.681%	$133.217	$133.22	$133.20	$133.20
Purchase #7	$69.79	12.162%	$78.2779	$78.28	$78.30	$78.30
7 purchase totals =	$1,120.75		$1,227.7410	$1,227.75	$1,227.75	$1,227.80