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	$149.52	5.509%	$157.7571	$157.76	$157.75	$157.80
Purchase #2	$89.97	10.145%	$99.0975	$99.10	$99.10	$99.10
Purchase #3	$214.58	5.249%	$225.8433	$225.84	$225.85	$225.80
Purchase #4	$79.79	12.565%	$89.8156	$89.82	$89.80	$89.80
Purchase #5	$103.79	7.736%	$111.8192	$111.82	$111.80	$111.80
Purchase #6	$107.67	7.847%	$116.1189	$116.12	$116.10	$116.10
Purchase #7	$248.31	12.396%	$279.0905	$279.09	$279.10	$279.10
7 purchase totals =	$993.63		$1,079.5421	$1,079.55	$1,079.50	$1,079.50