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	$42.31	9.660%	$46.3971	$46.40	$46.40	$46.40
Purchase #2	$111.41	7.825%	$120.1278	$120.13	$120.15	$120.10
Purchase #3	$49.45	11.660%	$55.2159	$55.22	$55.20	$55.20
Purchase #4	$102.40	3.122%	$105.5969	$105.60	$105.60	$105.60
Purchase #5	$165.86	10.650%	$183.5241	$183.52	$183.50	$183.50
Purchase #6	$24.95	8.791%	$27.1434	$27.14	$27.15	$27.10
Purchase #7	$97.31	9.539%	$106.5924	$106.59	$106.60	$106.60
7 purchase totals =	$593.69		$644.5976	$644.60	$644.60	$644.50