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	$134.55	8.707%	$146.2653	$146.27	$146.25	$146.30
Purchase #2	$102.82	7.586%	$110.6199	$110.62	$110.60	$110.60
Purchase #3	$151.97	13.410%	$172.3492	$172.35	$172.35	$172.30
Purchase #4	$67.93	12.120%	$76.1631	$76.16	$76.15	$76.20
Purchase #5	$218.59	5.364%	$230.3152	$230.32	$230.30	$230.30
Purchase #6	$156.38	10.489%	$172.7827	$172.78	$172.80	$172.80
Purchase #7	$166.62	4.605%	$174.2929	$174.29	$174.30	$174.30
7 purchase totals =	$998.86		$1,082.7883	$1,082.79	$1,082.75	$1,082.80