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	$233.80	12.564%	$263.1746	$263.17	$263.15	$263.20
Purchase #2	$216.50	6.517%	$230.6093	$230.61	$230.60	$230.60
Purchase #3	$112.35	4.274%	$117.1518	$117.15	$117.15	$117.20
Purchase #4	$213.49	11.840%	$238.7672	$238.77	$238.75	$238.80
Purchase #5	$249.40	6.560%	$265.7606	$265.76	$265.75	$265.80
Purchase #6	$83.57	7.432%	$89.7809	$89.78	$89.80	$89.80
Purchase #7	$83.39	10.131%	$91.8382	$91.84	$91.85	$91.80
7 purchase totals =	$1,192.50		$1,297.0826	$1,297.08	$1,297.05	$1,297.20