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	$40.28	12.543%	$45.3323	$45.33	$45.35	$45.30
Purchase #2	$164.96	8.417%	$178.8447	$178.84	$178.85	$178.80
Purchase #3	$16.84	13.723%	$19.151	$19.15	$19.15	$19.20
Purchase #4	$181.79	4.754%	$190.4323	$190.43	$190.45	$190.40
Purchase #5	$90.94	12.866%	$102.6403	$102.64	$102.65	$102.60
Purchase #6	$43.81	10.760%	$48.524	$48.52	$48.50	$48.50
Purchase #7	$51.70	7.628%	$55.6437	$55.64	$55.65	$55.60
7 purchase totals =	$590.32		$640.5683	$640.55	$640.60	$640.40