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	$231.55	8.624%	$251.5189	$251.52	$251.50	$251.50
Purchase #2	$209.72	4.630%	$219.43	$219.43	$219.45	$219.40
Purchase #3	$49.85	7.152%	$53.4153	$53.42	$53.40	$53.40
Purchase #4	$77.75	13.768%	$88.4546	$88.45	$88.45	$88.50
Purchase #5	$159.26	12.806%	$179.6548	$179.65	$179.65	$179.70
Purchase #6	$99.75	12.469%	$112.1878	$112.19	$112.20	$112.20
Purchase #7	$62.47	4.442%	$65.2449	$65.24	$65.25	$65.20
7 purchase totals =	$890.35		$969.9063	$969.90	$969.90	$969.90