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	$48.94	13.588%	$55.59	$55.59	$55.60	$55.60
Purchase #2	$171.85	9.650%	$188.4335	$188.43	$188.45	$188.40
Purchase #3	$176.96	7.170%	$189.648	$189.65	$189.65	$189.60
Purchase #4	$232.55	4.678%	$243.4287	$243.43	$243.45	$243.40
Purchase #5	$135.85	13.205%	$153.789	$153.79	$153.80	$153.80
Purchase #6	$40.83	10.813%	$45.2449	$45.24	$45.25	$45.20
Purchase #7	$155.40	11.418%	$173.1436	$173.14	$173.15	$173.10
7 purchase totals =	$962.38		$1,049.2777	$1,049.27	$1,049.35	$1,049.10