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	$28.74	6.723%	$30.6722	$30.67	$30.65	$30.70
Purchase #2	$137.63	5.550%	$145.2685	$145.27	$145.25	$145.30
Purchase #3	$127.77	13.727%	$145.309	$145.31	$145.30	$145.30
Purchase #4	$106.40	4.590%	$111.2838	$111.28	$111.30	$111.30
Purchase #5	$135.51	11.781%	$151.4744	$151.47	$151.45	$151.50
Purchase #6	$65.35	12.270%	$73.3684	$73.37	$73.35	$73.40
Purchase #7	$200.31	6.636%	$213.6026	$213.60	$213.60	$213.60
7 purchase totals =	$801.71		$870.9789	$870.97	$870.90	$871.10