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	$139.53	13.393%	$158.2173	$158.22	$158.20	$158.20
Purchase #2	$40.64	11.115%	$45.1571	$45.16	$45.15	$45.20
Purchase #3	$245.79	4.123%	$255.9239	$255.92	$255.90	$255.90
Purchase #4	$164.41	5.802%	$173.9491	$173.95	$173.95	$173.90
Purchase #5	$54.81	11.665%	$61.2036	$61.20	$61.20	$61.20
Purchase #6	$46.90	3.868%	$48.7141	$48.71	$48.70	$48.70
Purchase #7	$153.85	10.266%	$169.6442	$169.64	$169.65	$169.60
7 purchase totals =	$845.93		$912.8093	$912.80	$912.75	$912.70