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	$165.72	8.644%	$180.0448	$180.04	$180.05	$180.00
Purchase #2	$124.35	5.239%	$130.8647	$130.86	$130.85	$130.90
Purchase #3	$148.55	11.810%	$166.0938	$166.09	$166.10	$166.10
Purchase #4	$73.37	12.803%	$82.7636	$82.76	$82.75	$82.80
Purchase #5	$51.70	5.401%	$54.4923	$54.49	$54.50	$54.50
Purchase #6	$144.79	4.323%	$151.0493	$151.05	$151.05	$151.00
Purchase #7	$89.40	11.189%	$99.403	$99.40	$99.40	$99.40
7 purchase totals =	$797.88		$864.7115	$864.69	$864.70	$864.70