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	$66.48	10.290%	$73.3208	$73.32	$73.30	$73.30
Purchase #2	$41.58	10.402%	$45.9052	$45.91	$45.90	$45.90
Purchase #3	$51.50	7.112%	$55.1627	$55.16	$55.15	$55.20
Purchase #4	$121.64	4.548%	$127.1722	$127.17	$127.15	$127.20
Purchase #5	$158.48	4.522%	$165.6465	$165.65	$165.65	$165.60
Purchase #6	$176.52	13.543%	$200.4261	$200.43	$200.45	$200.40
Purchase #7	$10.97	9.520%	$12.0143	$12.01	$12.00	$12.00
7 purchase totals =	$627.17		$679.6478	$679.65	$679.60	$679.60