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	$53.76	3.238%	$55.5007	$55.50	$55.50	$55.50
Purchase #2	$146.41	9.692%	$160.6001	$160.60	$160.60	$160.60
Purchase #3	$192.29	4.341%	$200.6373	$200.64	$200.65	$200.60
Purchase #4	$236.37	12.746%	$266.4977	$266.50	$266.50	$266.50
Purchase #5	$102.62	8.515%	$111.3581	$111.36	$111.35	$111.40
Purchase #6	$187.94	10.742%	$208.1285	$208.13	$208.15	$208.10
Purchase #7	$217.83	10.409%	$240.5039	$240.50	$240.50	$240.50
7 purchase totals =	$1,137.22		$1,243.2263	$1,243.23	$1,243.25	$1,243.20