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	$198.52	8.540%	$215.4736	$215.47	$215.45	$215.50
Purchase #2	$133.93	8.666%	$145.5364	$145.54	$145.55	$145.50
Purchase #3	$11.75	12.689%	$13.241	$13.24	$13.25	$13.20
Purchase #4	$26.34	11.201%	$29.2903	$29.29	$29.30	$29.30
Purchase #5	$127.96	7.515%	$137.5762	$137.58	$137.60	$137.60
Purchase #6	$105.54	5.757%	$111.6159	$111.62	$111.60	$111.60
Purchase #7	$135.96	7.496%	$146.1516	$146.15	$146.15	$146.20
7 purchase totals =	$740.00		$798.8850	$798.89	$798.90	$798.90