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	$30.76	9.145%	$33.573	$33.57	$33.55	$33.60
Purchase #2	$222.94	11.447%	$248.4599	$248.46	$248.45	$248.50
Purchase #3	$52.52	9.509%	$57.5141	$57.51	$57.50	$57.50
Purchase #4	$98.29	13.667%	$111.7233	$111.72	$111.70	$111.70
Purchase #5	$134.28	9.564%	$147.1225	$147.12	$147.10	$147.10
Purchase #6	$246.88	12.848%	$278.5991	$278.60	$278.60	$278.60
Purchase #7	$13.39	6.166%	$14.2156	$14.22	$14.20	$14.20
7 purchase totals =	$799.06		$891.2075	$891.20	$891.10	$891.20