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	$138.32	13.704%	$157.2754	$157.28	$157.30	$157.30
Purchase #2	$80.70	11.465%	$89.9523	$89.95	$89.95	$90.00
Purchase #3	$62.66	11.860%	$70.0915	$70.09	$70.10	$70.10
Purchase #4	$215.26	11.342%	$239.6748	$239.67	$239.65	$239.70
Purchase #5	$67.64	13.253%	$76.6043	$76.60	$76.60	$76.60
Purchase #6	$123.53	3.149%	$127.42	$127.42	$127.40	$127.40
Purchase #7	$57.75	6.645%	$61.5875	$61.59	$61.60	$61.60
7 purchase totals =	$745.86		$822.6058	$822.60	$822.60	$822.70