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	$99.56	12.212%	$111.7183	$111.72	$111.70	$111.70
Purchase #2	$43.42	7.831%	$46.8202	$46.82	$46.80	$46.80
Purchase #3	$198.67	13.730%	$225.9474	$225.95	$225.95	$225.90
Purchase #4	$236.37	5.549%	$249.4862	$249.49	$249.50	$249.50
Purchase #5	$45.78	6.585%	$48.7946	$48.79	$48.80	$48.80
Purchase #6	$126.80	5.487%	$133.7575	$133.76	$133.75	$133.80
Purchase #7	$231.46	12.670%	$260.786	$260.79	$260.80	$260.80
7 purchase totals =	$982.06		$1,077.3102	$1,077.32	$1,077.30	$1,077.30