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	$135.71	11.337%	$151.0954	$151.10	$151.10	$151.10
Purchase #2	$225.77	11.571%	$251.8938	$251.89	$251.90	$251.90
Purchase #3	$215.90	10.691%	$238.9819	$238.98	$239.00	$239.00
Purchase #4	$57.45	11.487%	$64.0493	$64.05	$64.05	$64.00
Purchase #5	$119.79	12.118%	$134.3062	$134.31	$134.30	$134.30
Purchase #6	$223.42	6.149%	$237.1581	$237.16	$237.15	$237.20
Purchase #7	$90.82	13.752%	$103.3096	$103.31	$103.30	$103.30
7 purchase totals =	$1,068.86		$1,180.7943	$1,180.80	$1,180.80	$1,180.80