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	$230.32	9.584%	$252.3939	$252.39	$252.40	$252.40
Purchase #2	$107.79	7.690%	$116.0791	$116.08	$116.10	$116.10
Purchase #3	$65.60	10.661%	$72.5936	$72.59	$72.60	$72.60
Purchase #4	$156.34	6.705%	$166.8226	$166.82	$166.80	$166.80
Purchase #5	$111.66	4.112%	$116.2515	$116.25	$116.25	$116.30
Purchase #6	$133.65	4.332%	$139.4397	$139.44	$139.45	$139.40
Purchase #7	$176.60	6.578%	$188.2167	$188.22	$188.20	$188.20
7 purchase totals =	$981.96		$1,051.7971	$1,051.79	$1,051.80	$1,051.80