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	$25.87	11.531%	$28.8531	$28.85	$28.85	$28.90
Purchase #2	$10.55	12.309%	$11.8486	$11.85	$11.85	$11.80
Purchase #3	$116.52	5.383%	$122.7923	$122.79	$122.80	$122.80
Purchase #4	$104.40	9.604%	$114.4266	$114.43	$114.45	$114.40
Purchase #5	$86.49	3.275%	$89.3225	$89.32	$89.30	$89.30
Purchase #6	$30.29	7.843%	$32.6656	$32.67	$32.65	$32.70
Purchase #7	$88.43	5.826%	$93.5819	$93.58	$93.60	$93.60
7 purchase totals =	$462.55		$493.4906	$493.49	$493.50	$493.50