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	$64.55	5.583%	$68.1538	$68.15	$68.15	$68.20
Purchase #2	$139.46	13.403%	$158.1518	$158.15	$158.15	$158.20
Purchase #3	$85.80	5.437%	$90.4649	$90.46	$90.45	$90.50
Purchase #4	$114.32	3.583%	$118.4161	$118.42	$118.40	$118.40
Purchase #5	$193.45	13.780%	$220.1074	$220.11	$220.10	$220.10
Purchase #6	$134.98	6.700%	$144.0237	$144.02	$144.00	$144.00
Purchase #7	$50.39	11.818%	$56.3451	$56.35	$56.35	$56.30
7 purchase totals =	$782.95		$855.6628	$855.66	$855.60	$855.70