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	$142.46	9.464%	$155.9424	$155.94	$155.95	$155.90
Purchase #2	$187.76	11.329%	$209.0313	$209.03	$209.05	$209.00
Purchase #3	$193.87	11.167%	$215.5195	$215.52	$215.50	$215.50
Purchase #4	$138.73	7.362%	$148.9433	$148.94	$148.95	$148.90
Purchase #5	$79.58	10.732%	$88.1205	$88.12	$88.10	$88.10
Purchase #6	$89.27	11.663%	$99.6816	$99.68	$99.70	$99.70
Purchase #7	$230.83	13.536%	$262.0751	$262.08	$262.10	$262.10
7 purchase totals =	$1,062.50		$1,179.3137	$1,179.31	$1,179.35	$1,179.20