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	$239.79	3.648%	$248.5375	$248.54	$248.55	$248.50
Purchase #2	$43.71	6.396%	$46.5057	$46.51	$46.50	$46.50
Purchase #3	$9.94	4.802%	$10.4173	$10.42	$10.40	$10.40
Purchase #4	$98.82	6.688%	$105.4291	$105.43	$105.45	$105.40
Purchase #5	$221.82	5.482%	$233.9802	$233.98	$234.00	$234.00
Purchase #6	$248.97	7.181%	$266.8485	$266.85	$266.85	$266.80
Purchase #7	$89.61	5.799%	$94.8065	$94.81	$94.80	$94.80
7 purchase totals =	$952.66		$1,006.5248	$1,006.54	$1,006.55	$1,006.40