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	$238.46	13.194%	$269.9224	$269.92	$269.90	$269.90
Purchase #2	$96.92	7.715%	$104.3974	$104.40	$104.40	$104.40
Purchase #3	$82.85	4.577%	$86.642	$86.64	$86.65	$86.60
Purchase #4	$122.37	4.439%	$127.802	$127.80	$127.80	$127.80
Purchase #5	$11.91	12.728%	$13.4259	$13.43	$13.45	$13.40
Purchase #6	$38.73	12.852%	$43.7076	$43.71	$43.70	$43.70
Purchase #7	$221.91	8.756%	$241.3404	$241.34	$241.35	$241.30
7 purchase totals =	$813.15		$887.2377	$887.24	$887.25	$887.10