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	$125.74	10.152%	$138.5051	$138.51	$138.50	$138.50
Purchase #2	$61.99	13.412%	$70.3041	$70.30	$70.30	$70.30
Purchase #3	$12.98	11.581%	$14.4832	$14.48	$14.50	$14.50
Purchase #4	$153.42	13.766%	$174.5398	$174.54	$174.55	$174.50
Purchase #5	$100.98	11.161%	$112.2504	$112.25	$112.25	$112.30
Purchase #6	$90.29	10.167%	$99.4698	$99.47	$99.45	$99.50
Purchase #7	$27.84	4.757%	$29.1643	$29.16	$29.15	$29.20
7 purchase totals =	$573.24		$638.7167	$638.71	$638.70	$638.80