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	$45.35	13.724%	$51.5738	$51.57	$51.55	$51.60
Purchase #2	$173.47	10.450%	$191.5976	$191.60	$191.60	$191.60
Purchase #3	$113.90	5.736%	$120.4333	$120.43	$120.45	$120.40
Purchase #4	$76.45	4.685%	$80.0317	$80.03	$80.05	$80.00
Purchase #5	$155.38	12.535%	$174.8569	$174.86	$174.85	$174.90
Purchase #6	$137.79	3.796%	$143.0205	$143.02	$143.00	$143.00
Purchase #7	$75.44	9.549%	$82.6438	$82.64	$82.65	$82.60
7 purchase totals =	$777.78		$844.1576	$844.15	$844.15	$844.10