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	$103.61	11.162%	$115.1749	$115.17	$115.15	$115.20
Purchase #2	$235.50	9.324%	$257.458	$257.46	$257.45	$257.50
Purchase #3	$33.38	12.194%	$37.4504	$37.45	$37.45	$37.50
Purchase #4	$87.43	4.169%	$91.075	$91.08	$91.10	$91.10
Purchase #5	$120.88	5.820%	$127.9152	$127.92	$127.90	$127.90
Purchase #6	$126.39	8.489%	$137.1192	$137.12	$137.10	$137.10
Purchase #7	$152.99	13.670%	$173.9037	$173.90	$173.90	$173.90
7 purchase totals =	$860.18		$940.0964	$940.10	$940.05	$940.20