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	$116.48	3.710%	$120.8014	$120.80	$120.80	$120.80
Purchase #2	$226.46	5.365%	$238.6096	$238.61	$238.60	$238.60
Purchase #3	$113.80	12.321%	$127.8213	$127.82	$127.80	$127.80
Purchase #4	$72.54	13.363%	$82.2335	$82.23	$82.25	$82.20
Purchase #5	$170.68	11.157%	$189.7228	$189.72	$189.70	$189.70
Purchase #6	$202.61	12.565%	$228.0679	$228.07	$228.05	$228.10
Purchase #7	$146.65	13.253%	$166.0855	$166.09	$166.10	$166.10
7 purchase totals =	$1,049.22		$1,153.3420	$1,153.34	$1,153.30	$1,153.30