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	$31.88	9.278%	$34.8378	$34.84	$34.85	$34.80
Purchase #2	$101.66	13.693%	$115.5803	$115.58	$115.60	$115.60
Purchase #3	$120.75	5.687%	$127.6171	$127.62	$127.60	$127.60
Purchase #4	$139.86	8.350%	$151.5383	$151.54	$151.55	$151.50
Purchase #5	$150.30	5.313%	$158.2854	$158.29	$158.30	$158.30
Purchase #6	$200.44	10.274%	$221.0332	$221.03	$221.05	$221.00
Purchase #7	$207.90	12.298%	$233.4675	$233.47	$233.45	$233.50
7 purchase totals =	$952.79		$1,042.3596	$1,042.37	$1,042.40	$1,042.30