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	$77.38	6.189%	$82.169	$82.17	$82.15	$82.20
Purchase #2	$197.88	9.683%	$217.0407	$217.04	$217.05	$217.00
Purchase #3	$140.90	8.172%	$152.4143	$152.41	$152.40	$152.40
Purchase #4	$207.26	12.795%	$233.7789	$233.78	$233.80	$233.80
Purchase #5	$108.56	7.355%	$116.5446	$116.54	$116.55	$116.50
Purchase #6	$151.56	5.283%	$159.5669	$159.57	$159.55	$159.60
Purchase #7	$12.56	6.106%	$13.3269	$13.33	$13.35	$13.30
7 purchase totals =	$896.10		$974.8413	$974.84	$974.85	$974.80