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	$179.76	3.246%	$185.595	$185.60	$185.60	$185.60
Purchase #2	$248.58	7.122%	$266.2839	$266.28	$266.30	$266.30
Purchase #3	$243.96	6.559%	$259.9613	$259.96	$259.95	$260.00
Purchase #4	$20.52	6.299%	$21.8126	$21.81	$21.80	$21.80
Purchase #5	$100.92	11.723%	$112.7509	$112.75	$112.75	$112.80
Purchase #6	$19.71	8.323%	$21.3505	$21.35	$21.35	$21.40
Purchase #7	$174.46	7.836%	$188.1307	$188.13	$188.15	$188.10
7 purchase totals =	$987.91		$1,055.8849	$1,055.88	$1,055.90	$1,056.00