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	$217.61	10.208%	$239.8236	$239.82	$239.80	$239.80
Purchase #2	$31.64	4.849%	$33.1742	$33.17	$33.15	$33.20
Purchase #3	$50.38	5.640%	$53.2214	$53.22	$53.20	$53.20
Purchase #4	$19.30	7.667%	$20.7797	$20.78	$20.80	$20.80
Purchase #5	$242.78	3.547%	$251.3914	$251.39	$251.40	$251.40
Purchase #6	$59.60	6.763%	$63.6307	$63.63	$63.65	$63.60
Purchase #7	$111.69	10.261%	$123.1505	$123.15	$123.15	$123.20
7 purchase totals =	$733.00		$785.1715	$785.16	$785.15	$785.20