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	$166.51	4.103%	$173.3419	$173.34	$173.35	$173.30
Purchase #2	$116.88	3.116%	$120.522	$120.52	$120.50	$120.50
Purchase #3	$43.68	7.217%	$46.8324	$46.83	$46.85	$46.80
Purchase #4	$198.45	10.735%	$219.7536	$219.75	$219.75	$219.80
Purchase #5	$71.73	10.571%	$79.3126	$79.31	$79.30	$79.30
Purchase #6	$186.27	7.169%	$199.6237	$199.62	$199.60	$199.60
Purchase #7	$179.83	11.221%	$200.0087	$200.01	$200.00	$200.00
7 purchase totals =	$963.35		$1,039.3949	$1,039.38	$1,039.35	$1,039.30