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	$19.45	9.857%	$21.3672	$21.37	$21.35	$21.40
Purchase #2	$124.72	5.202%	$131.2079	$131.21	$131.20	$131.20
Purchase #3	$29.74	4.810%	$31.1705	$31.17	$31.15	$31.20
Purchase #4	$105.47	3.305%	$108.9558	$108.96	$108.95	$109.00
Purchase #5	$22.49	13.484%	$25.5226	$25.52	$25.50	$25.50
Purchase #6	$158.38	12.717%	$178.5212	$178.52	$178.50	$178.50
Purchase #7	$230.31	10.624%	$254.7781	$254.78	$254.80	$254.80
7 purchase totals =	$690.56		$751.5233	$751.53	$751.45	$751.60