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	$90.87	9.289%	$99.3109	$99.31	$99.30	$99.30
Purchase #2	$96.78	4.192%	$100.837	$100.84	$100.85	$100.80
Purchase #3	$165.93	10.749%	$183.7658	$183.77	$183.75	$183.80
Purchase #4	$153.68	8.421%	$166.6214	$166.62	$166.60	$166.60
Purchase #5	$126.82	13.181%	$143.5361	$143.54	$143.55	$143.50
Purchase #6	$39.29	10.383%	$43.3695	$43.37	$43.35	$43.40
Purchase #7	$24.44	11.448%	$27.2379	$27.24	$27.25	$27.20
7 purchase totals =	$697.81		$764.6786	$764.69	$764.65	$764.60