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	$40.32	12.464%	$45.3455	$45.35	$45.35	$45.30
Purchase #2	$47.56	11.446%	$53.0037	$53.00	$53.00	$53.00
Purchase #3	$192.45	9.622%	$210.9675	$210.97	$210.95	$211.00
Purchase #4	$42.91	7.723%	$46.2239	$46.22	$46.20	$46.20
Purchase #5	$166.54	3.775%	$172.8269	$172.83	$172.85	$172.80
Purchase #6	$129.39	10.485%	$142.9565	$142.96	$142.95	$143.00
Purchase #7	$220.86	9.247%	$241.2829	$241.28	$241.30	$241.30
7 purchase totals =	$840.03		$912.6069	$912.61	$912.60	$912.60