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	$115.60	4.226%	$120.4853	$120.49	$120.50	$120.50
Purchase #2	$137.72	7.448%	$147.9774	$147.98	$148.00	$148.00
Purchase #3	$222.68	3.646%	$230.7989	$230.80	$230.80	$230.80
Purchase #4	$160.28	3.654%	$166.1366	$166.14	$166.15	$166.10
Purchase #5	$92.94	13.319%	$105.3187	$105.32	$105.30	$105.30
Purchase #6	$56.42	10.753%	$62.4868	$62.49	$62.50	$62.50
Purchase #7	$73.92	6.685%	$78.8616	$78.86	$78.85	$78.90
7 purchase totals =	$859.56		$912.0653	$912.08	$912.10	$912.10