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	$93.69	6.520%	$99.7986	$99.80	$99.80	$99.80
Purchase #2	$227.78	11.792%	$254.6398	$254.64	$254.65	$254.60
Purchase #3	$90.89	13.492%	$103.1529	$103.15	$103.15	$103.20
Purchase #4	$145.64	5.279%	$153.3283	$153.33	$153.35	$153.30
Purchase #5	$200.53	13.474%	$227.5494	$227.55	$227.55	$227.50
Purchase #6	$172.25	6.784%	$183.9354	$183.94	$183.95	$183.90
Purchase #7	$231.78	10.723%	$256.6338	$256.63	$256.65	$256.60
7 purchase totals =	$1,162.56		$1,279.0382	$1,279.04	$1,279.10	$1,278.90