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	$165.53	8.493%	$179.5885	$179.59	$179.60	$179.60
Purchase #2	$161.25	13.810%	$183.5186	$183.52	$183.50	$183.50
Purchase #3	$141.30	8.659%	$153.5352	$153.54	$153.55	$153.50
Purchase #4	$64.28	7.574%	$69.1486	$69.15	$69.15	$69.10
Purchase #5	$173.31	3.466%	$179.3169	$179.32	$179.30	$179.30
Purchase #6	$120.70	5.866%	$127.7803	$127.78	$127.80	$127.80
Purchase #7	$35.52	7.765%	$38.2781	$38.28	$38.30	$38.30
7 purchase totals =	$861.89		$931.1662	$931.18	$931.20	$931.10