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	$48.99	13.153%	$55.4337	$55.43	$55.45	$55.40
Purchase #2	$18.30	7.305%	$19.6368	$19.64	$19.65	$19.60
Purchase #3	$139.52	12.159%	$156.4842	$156.48	$156.50	$156.50
Purchase #4	$9.63	10.514%	$10.6425	$10.64	$10.65	$10.60
Purchase #5	$250.29	6.292%	$266.0382	$266.04	$266.05	$266.00
Purchase #6	$80.50	12.154%	$90.284	$90.28	$90.30	$90.30
Purchase #7	$77.69	6.605%	$82.8214	$82.82	$82.80	$82.80
7 purchase totals =	$624.92		$681.3408	$681.33	$681.40	$681.20