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	$209.50	6.144%	$222.3717	$222.37	$222.35	$222.40
Purchase #2	$116.45	9.789%	$127.8493	$127.85	$127.85	$127.80
Purchase #3	$183.30	9.535%	$200.7777	$200.78	$200.80	$200.80
Purchase #4	$250.60	7.357%	$269.0366	$269.04	$269.05	$269.00
Purchase #5	$220.45	4.391%	$230.13	$230.13	$230.15	$230.10
Purchase #6	$164.74	13.345%	$186.7246	$186.72	$186.70	$186.70
Purchase #7	$133.70	7.495%	$143.7208	$143.72	$143.70	$143.70
7 purchase totals =	$1,278.74		$1,380.6107	$1,380.61	$1,380.60	$1,380.50