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	$131.34	10.112%	$144.6211	$144.62	$144.60	$144.60
Purchase #2	$128.32	7.747%	$138.261	$138.26	$138.25	$138.30
Purchase #3	$77.87	12.305%	$87.4519	$87.45	$87.45	$87.50
Purchase #4	$96.93	13.583%	$110.096	$110.10	$110.10	$110.10
Purchase #5	$80.59	6.326%	$85.6881	$85.69	$85.70	$85.70
Purchase #6	$72.82	11.123%	$80.9198	$80.92	$80.90	$80.90
Purchase #7	$17.36	5.589%	$18.3303	$18.33	$18.35	$18.30
7 purchase totals =	$605.23		$665.3682	$665.37	$665.35	$665.40